Patent Publication Number: US-2023146931-A1

Title: Authentication surface feature in additive manufacturing

Description:
BACKGROUND 
     Additive manufacturing may revolutionize design and manufacturing in producing three-dimensional (3D) objects. Some forms of additive manufacturing may sometimes be referred to as 3D printing, and may produce 3D objects with various surface characteristics. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a block diagram schematically representing an example device and/or example method of additively manufacturing an example 3D object to include an example first exterior surface portion including an example authentication surface feature. 
         FIG.  2    is a diagram including a top elevational view schematically representing an example first exterior surface portion including an example authentication surface feature. 
         FIG.  3    is a diagram including a side view schematically representing a portion of an example first exterior surface portion including an example authentication surface feature. 
         FIG.  4    is a block diagram schematically representing an example device and/or example method to additively manufacture a 3D object. 
         FIG.  5 A  is diagram including a top sectional view schematically representing an example embedded portion of a partially formed example 3D object. 
         FIG.  5 B  is diagram including a top elevational view schematically representing an example first exterior surface portion, including an example authentication surface feature, of an example 3D object. 
         FIG.  6    is diagram including a front elevational view schematically representing an example 3D object, which includes a first exterior surface portion comprising an authentication surface feature. 
         FIG.  7 A  is a diagram including a side sectional view schematically representing an example 3D object, including an example first interior portion including an example embedded portion. 
         FIG.  7 B  is diagram including a top elevational view schematically representing an example first exterior surface portion, including an example authentication surface feature, of an example 3D object. 
         FIG.  8    is a diagram including a block diagram schematically representing a device to obtain, store, and/or evaluate images of an authentication surface feature of a 3D object. 
         FIG.  9 A  is block diagram schematically representing an example object formation engine. 
         FIG.  9 B  is block diagram schematically representing an example control portion. 
         FIG.  9 C  is a block diagram schematically representing an example user interface. 
         FIG.  10 A  is flow diagram schematically representing an example method of additively manufacturing a 3D object with a surface feature variation for authentication. 
         FIG.  10 B  is a diagram schematically representing an example method of obtaining and storing images of a surface feature variation of an additively manufactured 3D object. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific examples in which the disclosure may be practiced. It is to be understood that other examples may be utilized and structural or logical changes may be made without departing from the scope of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense. It is to be understood that features of the various examples described herein may be combined, in part or whole, with each other, unless specifically noted otherwise. 
     At least some examples of the present disclosure provide for additively manufacturing a 3D object to include a first interior portion having a first thermal history different from a second thermal history of at least second interior portions surrounding the first interior portion to induce an authentication surface feature at a first exterior surface portion overlying the first interior portion. 
     In some examples, the first interior portion comprises an embedded portion which, in some examples, may comprise a first degree of fusion selectably different from a degree of fusion of the second interior portions. The first degree of fusion may be implemented by altering a volume of fusing agent and/or detailing agent applied to the build material which forms the embedded portion, such that the embedded portion may comprise unfused build material or partially fused build material. In some such examples, all of the build material forming the embedded portion may comprise the same degree of fusion, whether all the build material is unfused or all of the build material comprises the same degree of partial fusion. 
     However, in some examples the device can control a degree of fusion on a voxel-by-voxel basis, via controlling a volume and/or location of application of the fusing agent and/or detailing agent. Accordingly, in some examples the embedded portion may comprise a non-uniform array of voxel locations in which some voxel locations comprise unfused build material and some voxels locations comprise partially fused build material. Moreover, in some such examples, the non-uniform array of voxel locations may comprise some voxel locations with fully fused build material along with some voxel locations which are unfused and/or which are partially fused. 
     In some examples, a device and/or method comprises selecting a location, shape, and/or volume of the embedded portion, which also may specify a depth of the embedded portion relative to an exterior surface portion of the 3D object at which an authentication surface feature will appear. 
     These arrangements will produce a first thermal history for the first interior portion which is different from a second thermal history of second interior portions which surround the first interior portion, wherein the second thermal history is generally uniform and thereby results in a generally uniform exterior surface appearance at a second exterior surface portion surrounding the first exterior surface portion defined by the authentication surface feature. 
     In remaining unfused or becoming just partially fused, the embedded portion (at least partially defining the first interior portion) does not experience the same degree of thermal energy as the surrounding second interior portions, and subsequent additive layers (of the first interior portion) above the embedded portion will experience different thermal characteristics from subsequent additive layers of the surrounding second interior portions. Assuming that the embedded portion is formed at an appropriate depth, this altered thermal profile of the first interior portion will ultimately influence the last or top additive layer overlying the first interior portion (including embedded portion) such that the last or top layer will become overfused and thereby exhibit the random characteristics exhibited by the authentication surface feature. Such random characteristics may comprise variations in the surface appearance (as compared to a uniform appearance) regarding a color, shape, area, topography, degree of powder attachment, and the like. In some examples, the color variations may be grey-scale variations and/or different hues in a color space (e.g. CYMK). In some examples, the authentication surface feature may sometimes be referred to as an authentication surface mark, authentication surface colorization, surface feature variation, and the like. 
     A selectable variability in the degree of fusion of, and/or selectable variability in the location, shape, and volume of, the embedded portion facilitates randomness in the thermal history of the first interior portion, including layers overlying the embedded portion. The randomness of the thermal history may contribute to the randomness of characteristics, such as a color, shape, area, etc. of the authentication surface feature overlying the first interior portion (including the embedded portion). The randomness of these characteristics makes it much more difficult, if not impossible, for a counterfeiter to reproduce the authentication surface feature of the 3D object. 
     In some examples, the location, shape, and/or volume of the embedded portion as a whole (or some voxel locations therein) may be randomly selected. In some examples, the degree of fusion of the embedded portion as a whole (or some voxel locations therein) may be randomly selected, which may or may not occur in conjunction with random selection of the location, shape, and/or volume of the embedded portion. Such random selection may further contribute to the random characteristics of the surface authentication feature overlying the embedded portion of the first interior portion at least because such random selection influences the thermal history of the first interior portion in unpredictable ways. 
     Once a 3D object is formed according to the above-described examples, the 3D object will include a first exterior surface portion including an authentication surface feature. With this in mind, in some examples a device may be used to obtain and store images of the authentication surface feature for later use in authenticating a 3D object, and thereby preventing successful counterfeiting and/or deterring counterfeiting. 
     Accordingly, while the flexibility of additively manufacturing may tempt a counterfeiter to make counterfeit copies of particular 3D objects, the examples of the present disclosure provide a pathway to prevent success in such counterfeiting because of the irreproducibility of each unique authentication surface feature for any particular 3D object. 
     These examples, and additional examples, are further described in association with at least  FIGS.  1 - 10 B . 
       FIG.  1    is a diagram schematically representing an example device  50  (and/or method) to additively manufacture an example 3D object  100  including a first exterior surface portion  134  which includes an authentication surface feature  138 . As shown in  FIG.  1   , example 3D object  100  comprises opposite ends  102 A,  102 B, top  106 A, bottom  106 B, and a front side  104 A, opposite back side  104 B. 3D object  100  is additively formed beginning at the bottom (e.g.  106 B) and upward toward the top  106 A, as represented by directional arrow A. In some examples, the 3D object  100  in  FIG.  1    may be additively manufactured via at least some of the features and attributes of the device  200  described and illustrated later in association with at least  FIG.  4   . 
     In some examples, in order to facilitate future authentication of the 3D object  100 , during the layer-by-layer additive manufacturing of the 3D object  100 , a first interior portion  130  is caused to have a first thermal history which is different from a second thermal history of second interior portions  155  surrounding the first interior portion  130 . By doing so, a first exterior surface portion  134  overlying the first interior portion  130  will have an appearance different from a second exterior surface portion  112  overlying the second interior portions  155 , which surround the sides  133  of the first interior portion  130 . 
     In some examples, causing the first thermal history of the first interior portion  130  comprises modifying, in comparison to the surrounding second interior portions  155 , some characteristic of the additive manufacturing process in the first interior portion  130  underlying the expected first exterior surface portion  134 . In some examples, a modification may comprise an alteration in a volume of fusing agent and/or a detailing agent applied to the build material in forming the 3D object in the location of the first interior portion  130 . 
     For instance, as shown in  FIG.  1   , in some examples one modification may comprise forming an embedded portion  132  (shown in solid lines) at a bottom portion  135  of the first interior portion  130 , wherein the embedded portion  132  corresponds to a volume of build material which is unfused or partially fused. As a result, a degree of fusion of the embedded portion  132  is selectably different from a degree of fusion (e.g. fully fused) of the second interior portions  155  surrounding the embedded portion  132  (of the first interior portion  130 ). In some examples, the embedded portion  132  is formed by omitting application of a fusing agent and/or detailing agent, such that embedded portion  132  comprises free build material, such as free powder build material. In some examples, the embedded portion  132  may be formed by applying a reduced volume of fusing agent and/or detailing agent, such the build material of embedded portion  132  is just partially fused instead of being fully fused. 
     Once the embedded portion  132  is formed as part of one or several layers in additively manufacturing 3D object  100 , then subsequent layers of the 3D object (represented by portion  137  within dashed lines) will form the remainder of the interior portion  130 , which underlies the first exterior surface portion  134 . However, the subsequent layers forming the remaining portion ( 137 ) of the first interior portion  130  will experience a thermal history which no longer corresponds to a thermal history of the same subsequent layers in the surrounding second interior portions  155  surrounding the first interior portion  130 . Consequently, upon application of the last layer to additively form the exterior surface portion  110  of the top  106 A of the 3D object, the first exterior surface portion  134  overlying the first interior portion  130  will exhibit surface characteristics which are different from the surface characteristics of the second exterior surface portion  112  surrounding the first exterior surface portion  134 . The primary surface characteristics of the first exterior surface portion  134  include a change in color, which may be a change in grey-scale values or a change in hue (e.g. for a CYMK color space), as compared to a substantially uniform color of the surrounding second exterior surface portion  112 . 
     This surface feature variation apparent in the first surface exterior portion  134  will enable later authentication of the 3D object because of its uniqueness and irreproducibility. In particular, it would be difficult, if not impossible, for a counterfeiter to reproduce the exact same surface feature as first exterior portion  134  at least because the surface feature exhibits at least some random characteristics in view of how and why the first surface feature is generated. 
     As indicated by directional arrow B, the first exterior surface portion  134  is further illustrated schematically in  FIG.  1    and is further defined as authentication surface feature  138 , i.e. an authentication surface mark. It will be understood that an actual surface feature may not exhibit any particular pattern, and may exhibit a range of colors (e.g. grey scale values, hues, etc.), may have irregular borders, etc. Accordingly, it will be understood that the appearance of the authentication surface feature  138  in  FIG.  1    is merely for illustrative purposes and is not limiting regarding the shapes, sizes, colors, etc. of an actual surface feature for first exterior surface portion  134  because of its altered thermal history (as compared to the surrounding second interior portions  155 ). 
     In some examples, the authentication surface feature  138  may be characterized by its location, such as via x, y coordinates on the top portion  106 A of 3D object  100 , and/or characterized according to its size (e.g. area) which may include measurements of length (L) and/or width (W). The authentication surface feature  138  also may be characterized by greyscale levels, hues, patterns (or lack thereof), border shapes, etc. For example, one non-limiting example schematically representing an authentication surface feature  138  comprises portion  139 B juxtaposed with portion  139 A. As previously noted, this appearance comprises random characteristics not specifically selected upon initiating additive formation of the 3D object  100 , and not reproducible because of the random nature in the way such surface features are generated by causing an alteration in the thermal history of a first interior portion  130  of the 3D object  100 . As later described in association with at least  FIG.  8   , a device  681  including an imager  672  may be used to objectively identify the unique characteristics (e.g. location, size, area, colors, etc.) of the authentication surface feature  138  of the first exterior surface portion  134 , and/or of second exterior surface portions  112 . 
     It will be understood, from the foregoing examples and at least some following examples, that introducing an embedded portion  132  below the general exterior surface portion  110  of the 3D object  100  (as shown in  FIG.  1   ) is a modification made within the interior of the 3D object  100  to cause a change in the thermal history of portions (e.g.  137  in  FIG.  1   ) above the embedded portion  132 , which extend up to, and include an altered thermal history and behavior at the first exterior surface portion  134  at which the authentication surface feature  138  exhibits random surface characteristics. 
     However, in some examples, a modification also may include intentionally modifying the exterior surface portion  110  directly at the first exterior surface portion  134  (to cause some random surface feature characteristics) in addition to the previously described intentional modification of introducing the embedded portion  132  at some depth below the general exterior surface portion  110  (which includes the first exterior surface portion  134 ) in order to cause random surface characteristics. In some such examples, intentionally modifying both interior portions and exterior surface portions of the 3D object to cause an authentication surface feature (e.g.  138 ) may enhance the effectiveness of the authentication surface feature in becoming uniquely distinctive (by exhibiting random surface characteristics) and difficult to reproduce, thereby further hampering successful attempts at counterfeiting the 3D object (including its authentication surface feature). At least some of the uniqueness of the authentication surface feature arises from the random characteristics in thermal behavior caused by the intentional internal modification and the intentional external modification of thermal behavior and history associated with the first surface exterior portion  134 . It will be further understood that the example of intentionally modifying the exterior surface portion (e.g.  110 ) at a first exterior surface portion  134  (which overlies the embedded portion  132 ), in combination with the intentional internal modification implemented via the interiorly-located embedded portion  132 , may be applied to at least some of the later described examples of the present disclosure. 
       FIG.  2    is diagram  160  including a top plan view of an example authentication surface feature of a 3D object  161 . In some examples, the 3D object  161  may comprise a first interior portion like first interior portion  130  of 3D object  100  in  FIG.  1   , and yet result in an authentication surface feature  168  (at first exterior surface portion  134 ) which is different from the authentication surface feature  138  shown in  FIG.  1   . In one aspect, this situation arises from the development of random characteristics as subsequent layers forming first interior portion  130  are added above the embedded portion  132 . 
     However, in some examples, the first interior portion  130  may comprise a differently shaped and/or sized embedded portion  132 , or may comprise a different degree of fusion, etc. All of these variations would contribute to the development of random characteristics in the thermal history of a first interior portion, further ensuring that the resulting authentication surface feature will have a unique appearance. 
     As further shown in  FIG.  2   , the second exterior surface portion(s)  112 , which surround the authentication surface feature  168  at first surface exterior portion  134 , exhibit a substantially uniform appearance. 
     As shown in  FIG.  2   , in some examples the authentication surface feature  168  comprises portions  169 A,  169 B,  169 C which are juxtaposed with each other. As previously noted, this example surface feature is merely a simplistic schematic representation, wherein an actual surface feature may exhibit more complexity (or less complexity) in its shape, size, colors (e.g. gray-scale variations, hues), patterns, lack of pattern, randomness, etc. 
     As schematically represented in the side view of diagram  180 , in some examples, a first exterior surface portion  186  (including an authentication surface feature) may exhibit changes in a texture, porosity, etc., as represented by the irregular topography at surface portion  188  (of the first exterior surface portion  186 ) as compared to the relatively smooth surface portions  190  of the surrounding second exterior surface portion  112 . Accordingly, in some examples, such topographic variations may be present along with changes in color, shape, size, etc. associated with an authentication surface feature (e.g.  168  in  FIG.  2   ). 
     As further described later in association with at least  FIGS.  9 A- 10 B , in some examples, the operation of device  50  in  FIG.  1    may be embodied in the form of instructions stored in non-transitory machine-readable medium (and executable via a processor), while in some examples, a printer control portion may be programmed to cause such operation of device  50 . 
     It will be understood that an authentication surface feature  138 ,  168  may be implemented without changing the type or volume of build material for that first interior portion  130  (for which a modified thermal history will be produced) and/or without changing a boundary geometry of the 3D object in the region at which the first thermal history of the first interior portion (e.g.  130  in  FIG.  1   ) is being generated. 
       FIG.  4    is a diagram schematically representing an example device  200  to additively manufacture an example 3D object  280  including an authentication surface feature, such as provided via the examples previously described in association with at least  FIGS.  1 - 3   . Accordingly, the device  200  in  FIG.  4    may comprise one example implementation of the arrangement  50  in  FIG.  1    and/or comprise at least some of substantially the same features and attributes for additively manufacturing a 3D object as previously described in association with  FIGS.  1 - 3   . 
     As shown in  FIG.  4   , in some examples, the device  200  comprises a material distributor  250  and a fluid dispenser  258 . The material distributor  250  is arranged to dispense a build material layer-by-layer onto a build pad  242  to additively form the 3D object  280 . Once formed, the 3D object  280  may be separated from the build pad  242 . It will be understood that a 3D object of any shape and any size can be manufactured, and the object  280  depicted in  FIG.  4    provides just one example shape and size of a 3D object. In some instances device  200  may sometimes be referred to as a 3D printer. Accordingly, the build pad  242  may sometimes be referred to as a print bed or a receiving surface. 
     It will be understood that the material distributor  250  may be implemented via a variety of electromechanical or mechanical mechanisms, such as doctor blades, slot dies, extruders, and/or other structures suitable to spread, deposit, and/or otherwise form a coating of the build material in a generally uniform layer relative to the build pad  242  or relative to a previously deposited layer of build material. 
     In some examples, the material distributor  250  has a length (L 1 ) at least generally matching an entire length (L 1 ) of the build pad  242 , such that the material distributor  250  is capable of coating the entire build pad  242  with a layer  282 A of build material in a single pass as the material distributor  250  travels the width (W 1 ) of the build pad  242 . In some examples, the material distributor  250  can selectively deposit layers of material in lengths and patterns less than a full length of the material distributor  250 . In some examples, the material distributor  250  may coat the build pad  242  with a layer  282 A of build material(s) using multiple passes instead of a single pass. 
     It will be further understood that a 3D object additively formed via device  200  may have a width and/or a length less than a width (W 1 ) and/or length (L 1 ) of the build pad  242 . 
     In some examples, the material distributor  250  moves in a first orientation (represented by directional arrow F) while the fluid dispenser  258  moves in a second orientation (represented by directional arrow S) generally perpendicular to the first orientation. In some examples, the material distributor  250  can deposit material in each pass of a back-and-forth travel path along the first orientation while the fluid dispenser  258  can deposit fluid agents in each pass of a back-and-forth travel path along the second orientation. In at least some examples, one pass is completed by the material distributor  250 , followed by a pass of the fluid dispenser  258  before a second pass of the material distributor  250  is initiated, and so on. 
     In some examples, the material distributor  250  and the fluid dispenser  258  can be arranged to move in the same orientation, either the first orientation (F) or the second orientation (S). In some such examples, the material distributor  250  and the fluid dispenser  258  may be supported and moved via a single carriage while in some such examples, the material distributor  250  and dispenser  258  may be supported and moved via separate, independent carriages. 
     In some examples, the build material used to generally form the 3D object comprises a polymer material. In some examples, the polymer material comprises a polyamide material. However, a broad range of polymer materials (or their combinations) may be employed as the build material. In some examples, the build material may comprise a ceramic material. In some examples, the build material may take the form of a powder while in some examples, the build material may take a non-powder form, such as liquid or filament. Regardless of the particular form, at least some examples of the build material is suitable for spreading, depositing, extruding, flowing, etc. in a form to produce layers (via material distributor  250 ) additively relative to build pad  242  and/or relative to previously formed first layers of the build material. 
     In some examples, the fluid dispenser  258  shown in  FIG.  4    comprises a printing mechanism, such as an array of printheads, each including a plurality of individually addressable nozzles for selectively ejecting fluid agents onto a layer of build material. Accordingly, in some examples, the fluid dispenser  258  may sometimes be referred to as an addressable fluid ejection array. In some examples, the fluid dispenser  258  may eject individual droplets having a volume on the order of ones of picoliters or on the order of ones of nanoliters. 
     In some examples, fluid dispenser  258  comprises a thermal inkjet (TIJ) array. In some examples, fluid dispenser  258  may comprise a piezoelectric inkjet (PIJ) array or other technologies such as aerosol jetting, anyone of which can precisely, selectively deposit a small volume of fluid. In some examples, fluid dispenser  258  may comprise continuous inkjet technology. 
     In some examples, the fluid dispenser  258  selective dispenses droplets on a voxel-by-voxel basis. In one sense a voxel may be understood as a unit of volume in a three-dimensional space. In some examples, a resolution of 1200 voxels per inch in the x-y plane is implemented via fluid dispenser  258 . In some examples, a voxel may have a height H 2  (or thickness) of about 100 microns, although a height of the voxel may fall between about 80 microns and about 100 microns. However, in some examples, a height of a voxel may fall outside the range of about 80 to about 100 microns.  FIG.  4    also illustrates the fully formed 3D object  280  having a height H 1 . 
     In some examples, the height (H 2 ) of the voxel may correspond to a thickness of one layer (e.g.  282 A) of the build material. 
     In some examples, the fluid dispenser  258  has a width (W 1 ) at least generally matching an entire width (W 1 ) of the build pad  242 , and therefore may sometimes be referred to as providing page-wide manufacturing (e.g. page wide printing). In such examples, via this arrangement the fluid dispenser  258  can deposit fluid agents onto the entire receiving surface in a single pass as the fluid dispenser  258  travels the length (L 1 ) of the build pad  242 . In some examples, the fluid dispenser  258  may deposit fluid agents onto a given layer of material using multiple passes instead of a single pass. 
     In some examples, fluid dispenser  258  may comprise, or be in fluid communication with, an array of reservoirs to contain various fluid agents  262 . In some examples, the array of reservoirs may comprise a fluid supply  215 . In some examples, the fluid supply  215  comprises reservoirs to hold various fluids, such as a carrier (e.g. ink flux) by which various agents may be applied in a fluidic form. 
     In some examples, at least some of the fluid agents  262  may comprise a fusing agent, a color agent, detailing agent, etc. to enhance formation of each layer  282 A of build material. In particular, upon application onto the build material at selectable positions via the fluid dispenser  258 , the respective fusing agent and/or detailing agent may diffuse, saturate, and/or blend into the respective layer of the build material at the selectable positions. As noted elsewhere, a volume and/or location of application of the fusing agent and/or detailing agent on particular portions of the build material may be used to selectively control a degree of fusion (e.g. solidification), porosity, and/or density of the build material and therefore modify or control at least one thermal parameter (e.g. conductivity, heat capacity, specific heat capacity) of the particular portions of the build material. Moreover, by controlling these characteristics of the particular portions, one may control at least one thermal parameter of the entire 3D object or portions thereof. 
     As further shown in  FIG.  4   , in some examples, the at least partially formed 3D object  280  comprises a first portion  271 A and a second portion  271 B with dashed line  273  representing a boundary between the first portion  271 A and the second portion  271 B. The 3D object  280  may comprise an exterior side surface  288 . 
     During formation of a desired number of layers  282 A of the build material, in some examples the fluid dispenser  258  may selectively dispense droplets of fluid agent(s)  262  at some first selectable voxel locations  274  of at least some respective layers  282 A to at least partially define the first portion  271 A of the 3D object. It will be understood that a group  272  of first selectable voxel locations  274 , or multiple different groups  272  of first selectable voxel locations  274  may be selected in any position, any size, any shape, and/or combination of shapes. 
     In some examples, the at least some first selectable voxel locations  274  may correspond to an entire layer  282 A of a 3D object or just a portion of a layer  282 A. Meanwhile, in some examples, the 3D object may comprise a part of a larger object. In some examples, each first selectable voxel location  274  corresponds to a single voxel. 
     As further shown in  FIG.  4   , in some examples device  200  comprises an energy source  210  for applying energy (e.g. irradiating) to the deposited build materials, fluid agents (e.g. fusing agent, detailing agent, etc.) to cause heating of the material, which in turn results in the fusing of particles of the material relative to each other, with such fusing occurring via melting, sintering, etc. In portions of the 3D object in which full solidification is desired, such as for structural purposes, then a full volume of the respective fusing agents and/or detailing agents are applied to those portions of the 3D object. However, as noted elsewhere previously, in portions of the 3D object for which a modification at least one thermal parameter (e.g. conductivity, heat capacity, specific heat capacity) is to be implemented, then a lower volume of the respective fusing agent(s) and/or detailing agent(s) are to be applied. 
     After application of the radiation from energy source  210 , a layer  282 A of build material is formed and additional layers  282 A of build material may be formed in a similar manner as represented in  FIG.  4   . In view of the foregoing examples, it will be understood that any given formed layer  282 A of build material may include at least some portions which are unfused or partially fused in order to achieve the target thermal parameter objectives. 
     In some examples, the energy source  210  may comprise a gas discharge illuminant, such as but not limited to a Halogen lamp. In some examples, the energy source  210  may comprise multiple energy sources. As previously noted, energy source  210  may be stationary or mobile and may operate in a single flash or multiple flash mode. 
     As shown in  FIG.  4   , in some examples device  200  may comprise a control portion  217  to direct operations of device  200 . In some examples, control portion  217  may be implemented via at least some of substantially the same features and attributes as control portion  800 , as later described in association with at least  FIG.  9 B . 
     In some examples the device  200  in  FIG.  4    can be used to additively form a 3D object via a powder bed-based process, such as MultiJet Fusion (MJF) process (available from HP, Inc.). It will be understood that in some examples other additive manufacturing techniques (e.g. Fused Deposition Modeling (FDM), Selective Laser Sintering (SLS), Selective Laser Melting (SLM), 3D binder jetting, Electron Beam Melting (EBM), ProJet Fusion, etc.) may be used for form a 3D object. In such arrangements, the selectable parameter (e.g. porosity, density, fusion) and resulting thermal parameter in the portion  90  (according to examples of the present disclosure) may be implemented according to the particular build materials, application techniques, curing techniques, etc. associated with each particular modality of manufacturing. 
     With further reference to at least  FIGS.  1  and  4   , in some examples, an authentication surface feature (e.g.  138  in  FIG.  1   ) may be created with a first interior portion (e.g.  130  in  FIG.  1   )) which is not entirely surrounded by second interior portions (e.g.  155  in  FIG.  1   ), such as if one side of the first interior portion  130  were exposed on a portion (e.g. side  104 A) of the 3D object other than the side  106 A at which first exterior portion  134  (including authentication surface feature  138 ) is located. In such an arrangement, the second interior portions  155  partially surround the first interior portion  130  (and embedded portion  132 ) but do not completely surround the first interior portion  130 . In such arrangement, the embedded portion (e.g.  132 ) still influences the thermal history of the first interior portion  134  overlying the embedded portion  132 . In such arrangements, it will be further understood that the side (e.g.  104 A in  FIG.  1   ) of the interior portion  130  (including embedded portion  132 ) which is exposed on a surface of the 3D object may be fully fused to ensure structural integrity of the 3D object and to leave the surface appearance of the side (e.g.  104 A) of the 3D object unaltered. Meanwhile, other regions (e.g. a majority or super majority) of the first interior portion  130  (including the embedded portion  132 ) may be unfused or just partially fused to cause the alteration in the thermal history as compared to the second interior portions which to partially surround the first interior portion  130  (including the embedded portion  132 ). 
       FIG.  5 A  is a diagram  400  including a sectional view schematically representing an example partially formed 3D object  402 . In some examples, the partially formed 3D object  402  may be additively manufactured according to at least some of the same features and attributes as previously described in association with at least  FIGS.  1 - 4   . As shown in  FIG.  5 A , in some examples an embedded portion  415  of a first interior portion  430  has been additively formed to function in substantially the same manner as embedded portion  132  of first interior portion  130  in  FIG.  1   , except that in the example of  FIG.  5 A  the embedded portion  415  has a randomly generated volume and/or shape, which may further enhance the random characteristics exhibited by the authentication surface feature  438  of the first exterior surface portion  434  shown in  FIG.  5 B . This arrangement, in turn, may further prevent counterfeiting by making it even more difficult for a counterfeiter to reproduce the authentication surface feature  438  of the first exterior portion  434  of the 3D object  402 . 
     In some examples, the authentication surface feature  438  at the first exterior surface portion  434  comprises portions  439 A,  439 B,  439 C,  439 D, which are juxtaposed with each other to schematically represent random characteristics in a size, shape, location, grey-scale colorization of the random characteristics of the randomly-generated authentication surface feature  438  at the first exterior surface portion  434  of the 3D object  402 . 
     It will be understood that in some examples, the randomly-generated volume and/or shape of the embedded portion  415  in  FIG.  5 A  is bounded by a selectable maximum volume. In some examples, the selectable maximum volume may be implemented according to an array of three-dimensional coordinates (x, y, z). Within the three-dimensional coordinate array setting the maximum volume, the embedded portion (e.g.  132  in  FIG.  1 ,  632    in  FIG.  7 A ) may have any randomly-generated volume, shape, and/or location. Moreover, in some examples, the embedded portion  415  may be formed via randomly-varying amounts of the applied respective fusing agent and detailing agent at voxel locations ( 274 ) to cause a randomly-generated degree of fusion, which may enhance the generation of random characteristics of the authentication surface feature  438  at a first exterior surface portion  434  of the 3D object  402 . 
       FIG.  6    is diagram  600  including a front view of an example 3D object  602 . In some examples, the 3D object  602  is additively manufactured according to at least some of the same features and attributes as previously described in association with at least  FIGS.  1 - 5 B . In some examples, 3D object  602  may comprise a body portion  615 , head portion  616 , top exterior surface portion  610 , and opposite bottom exterior surface portion  614 . It will be understood that the particular configuration shown in  FIG.  6    is not limiting in that the sense that a 3D object associated with the examples relating to  FIGS.  6 - 8    may comprise a wide variety of shapes, sizes, configurations, purposes, etc. 
     While not visible in  FIG.  6   , in some examples the 3D object  602  includes an authentication surface feature of a first exterior surface portion (as in the previously described examples) at a region denoted by the box  620 . In one aspect, this region  620  is selected for the location of the authentication surface feature because it is relatively inconspicuous and will not generally affect the overall aesthetics of the 3D object. However, other more conspicuous locations on an exterior surface portion of the 3D object may be selected to bear an authentication surface feature as desired. 
       FIG.  7 A  is diagram including a side sectional view schematically representing the region represented by box  620  in  FIG.  6   , and which includes of a first exterior surface portion  634  including an authentication surface feature  638  ( FIG.  7 B ) for the 3D object  602 . In some examples, the region represented via box  620  may comprise a recess  640  formed in the bottom exterior surface portion  614  of 3D object  602 . 
     As shown in  FIG.  7 A , at region  620  the 3D object  602  comprises a first interior portion  630  including an embedded portion  632 , which function substantially the same as the first interior portion  130  and embedded portion  132 , respectively, in the example of  FIG.  1   . In some examples, the embedded portion  632  may comprise a selectable shape and/or volume (at the selected region  620 ), or may comprise a randomly-generated shape and/or volume at the selected location. In addition, the depth D may be selected or randomly-generated (within a selectable limit). 
     As further shown in  FIG.  7 A , the first interior portion  630  (represented via dashed lines) is surrounded by second interior portions  655  above which is an overlying second exterior surface portion  612 . The first interior portion  630  includes sides  633  (like sides  133  in  FIG.  1   ), and includes portion  637  (like portion  137  in  FIG.  1   ). The second exterior surface portion  612  forms part of a bottom exterior surface portion  614 , which is generally opposite a top exterior surface portion  610  of the 3D object  602 . 
       FIG.  7 B  is diagram  670  including a top view schematically representing one example implementation of a first exterior surface portion  634  of 3D object  602  ( FIG.  6   ), including an authentication surface feature  638 . As shown in  FIG.  7 B , the authentication surface feature  638  comprises portions  639 A,  639 B,  639 C, which schematically represent random characteristics of the authentication surface feature generated from the thermal history of first interior portion  630 , including embedded portion  632  shown in  FIG.  7 A . It will be understood that when a second identical 3D object (like  602  in  FIG.  6   ) is be additively manufactured including an embedded portion (e.g.  632  in  FIG.  7 A ) identical to the one which produced the first exterior surface portion  634  shown in  FIG.  7 B , the second 3D object will exhibit a first exterior surface portion  634  exhibiting an authentication surface feature different from the authentication surface feature schematically represented in  FIG.  7 B . Like the first exterior surface portion  634  in  FIG.  7 B , the first exterior surface portion  634  of the second identical 3D object will exhibit random characteristics in its shape, size (e.g. area), colorization, etc. but which are different from the random characteristics (in shape, size, colorization, etc.) for the first 3D object  602 . 
       FIG.  8    is a diagram  680  schematically representing an example device  681  to at least obtain and store images of an authentication surface feature from an authentic 3D object  602 . In some examples, the 3D object  602  may be additively manufactured according to a device and/or method comprising at least some of substantially the same features and attributes as the examples previously described in association with at least  FIGS.  1 - 7 B  so that the 3D object  602  will comprise a first surface exterior portion (e.g.  634  in  FIGS.  7 A- 7 B ) including an authentication surface feature (e.g.  638  in  FIG.  7 B ) 
     As shown in  FIG.  8   , in some examples, device  681  comprises an imager  684  and a data store  682 . After complete formation of an authentic 3D object  602 , the imager  684  is to obtain images of the first exterior surface portion (e.g.  634  in  FIG.  7 B ), including authentication surface feature (e.g.  638  in  FIG.  7 B ), and of at least some portion of the surrounding second surface exterior portions (e.g.  112  in  FIG.  1   ;  612  in  FIGS.  7 A- 7 B ). The obtained images of the respective first and second exterior portions  134 ,  112  of the authentic 3D object are stored in data store  682  for later use in authenticating, e.g. determining whether a particular 3D object is authentic. In such an arrangement, at a later time when it is desired to determine the authenticity of a candidate 3D object, the imager  684  is operated to obtain an image of an exterior surface portion of the candidate 3D object (e.g.  602 ) such as at a region denoted by box  620 . The obtained image  685  is compared to stored images in data store  682  to determine whether the exterior surface portion (e.g. like  634 ,  612 ) of the candidate 3D object captured in the obtained image includes a first exterior surface portion  634  (including an authentication surface feature  638  in  FIG.  7 B ) which matches a stored image, for an authentic 3D object, of a first exterior surface portion  634  (including an authentication surface feature  638  in  FIG.  7 B ). If there is a match, then the candidate 3D object may be deemed authentic, i.e. the same as the original authentic 3D object. If there is no match, then the candidate 3D object may be deemed inauthentic or a counterfeit, i.e. is not the same as the original, authentic object. 
     Similarly, as previously noted, one can obtain and store images of the second exterior surface portions  612  of a known authentic 3D object, which can later be compared with corresponding second exterior surface portions  612  of a candidate 3D object to determine whether the candidate 3D object is authentic or not. This comparison may be performed in conjunction with, or separate from, the comparison of the first exterior surface portions noted above. 
     It will be understood that in some examples, operation of the imager  684  and/or data store  682  may be implemented in association with a control portion, such as control portion  800  later described in association with  FIG.  9 B . In some such examples, at least a portion of control portion  800  may be incorporated into device  681 . In some examples, the data store  682  may comprise at least some of substantially the same features and attributes as memory  810  in  FIG.  9 B . 
       FIG.  9 A  is a block diagram schematically representing an example object formation engine  700 . In some examples, the object formation engine  700  may form part of a control portion  800 , as later described in association with at least  FIG.  9 B , such as but not limited to comprising at least part of the instructions  811 . In some examples, the object formation engine  700  may be used to implement at least some of the various example devices and/or example methods of the present disclosure as previously described in association with  FIGS.  1 - 8    and/or as later described in association with  FIGS.  9 B- 10 B . In some examples, the object formation engine  700  ( FIG.  9 A ) and/or control portion  800  ( FIG.  9 B ) may form part of, and/or be in communication with, an object formation device. Accordingly, in some examples, at least some aspects of control portion  800  may comprise one example implementation of the control portion  217  of device  200  in  FIG.  4   . 
     As shown in  FIG.  9 A , in some examples the object formation engine  700  may comprise a material distributor engine  702 , fluid dispenser engine  704 , energy source engine  706 . 
     As shown in  FIG.  9 A , in some examples the material distributor engine  702  controls distribution of layers of build material relative to build pad (e.g.  242  in  FIG.  4   ) and/or relative to previously deposited layers of build material. In some examples, the material distributor engine  702  comprises a material parameter to specify which material(s) and the quantity of such material which can be used to additively form a body of the 3D object. In some examples, these materials are deposited via build material distributor  250  of device  200  ( FIG.  4   ). 
     In some examples, the material controlled material distributor engine  702  may comprise polymers, ceramics, etc. having sufficient strength, formability, toughness, etc. for the intended use of the 3D object with at least some example materials being previously described in association with at least  FIG.  4   . 
     As shown in  FIG.  9 A , in some examples the fluid dispenser engine  704  may specify which fluid agents are to be selectively deposited onto a layer (or portions of a layer) of build material on a voxel-by-voxel basis, as previously described in association with at least  FIG.  4   . In some examples, such agents are deposited via fluid dispenser  258  ( FIG.  4   ). In some examples, the fluid dispenser engine  704  may comprise a carrier function and an agent function to apply fluid agents, such as the carrier, fusing, detailing, etc. as previously described in association with at least  FIG.  4   . 
     In particular, via the fluid dispenser engine  704 , application of a selectable volume (and location) of a fusing agent and/or detailing agent may be used to selectably control a degree of fusion at selectable voxel locations ( 274  in  FIG.  4   ). In some such examples, such control may be used to influence a thermal history of a portion of a 3D object to cause an authentication surface feature, as described in previous examples and as later further described in association with fusion parameter  750  of thermal history engine  730 . In some examples, fluid dispenser engine  704  may specify a number of fluid application channels, volume of fluid to be applied, during which pass the particular fluid channel is active, etc. 
     In some examples, the energy source engine  706  of object formation engine  700  is to control operations of at least one energy source (e.g.  210  in  FIG.  4   ). In some examples, the energy source engine  706  may control an amount of time that energy (e.g. radiation) from the energy source  210  ( FIG.  4   ) is emitted toward the material, agents, etc. on a layer of build material, with a resulting degree of fusion depending on a volume (and location) of fusing agent(s) and/or detailing agent(s) applied at particular voxel locations ( 274  in  FIG.  4   ). As further described later in association with fusion parameter  750  of the thermal history engine  730 , such control over a degree of fusion may be applied to an embedded portion (e.g.  132  in  FIG.  1   ;  632  in  FIG.  7 A ) to intentionally influence a thermal history of a first interior portion (e.g.  130  in  FIG.  1   ;  630  in  FIG.  7 A ) to produce an authentication surface feature (e.g.  138  in FIG.  1 ;  638  in  FIG.  7 B ). In some examples, the energy source  706  may irradiate the targeted layer (of the 3D object under formation) in a single flash or in multiple flashes. In some examples, the energy source may remain stationary (i.e. static) or may be mobile. In either case, during such irradiation, the energy source engine  706  controls the intensity, volume, and/or rate of irradiation. 
     As further shown in  FIG.  9 A , in some examples, the object formation engine  700  comprise a thermal history engine  730 , which is to control formation of at least an embedded portion (e.g.  132  in  FIG.  1 ,  632    in  FIG.  7 A ) to cause a resulting thermal history suited to produce a first exterior surface portion, including an authentication surface feature, as previously described in various examples throughout the present disclosure. Accordingly, in some examples, the thermal history engine  730  comprises an embedded portion engine  731  which is to control various aspects of forming an embedded portion. 
     In some examples, the embedded portion engine  731  comprises a location parameter  732 , a volume parameter  734 , a shape parameter  736 , a random parameter  740  and/or a fusion parameter  750 . 
     In some examples, in order to produce a first exterior surface portion (e.g.  134  in  FIG.  1   ;  634  in  FIG.  7 B ) including an authentication surface feature (e.g.  138  in  FIG.  1   ;  638  in  FIG.  7 B ), an embedded portion (e.g.  132  in  FIG.  1   ;  632  in  FIG.  7 A ) may be implemented to have a selectable location (parameter  732 ), volume (parameter  734 ), and/or shape (parameter  736 ) within a 3D object (e.g.  602 ). In some such examples, the volume can be specified as an absolute volume or as a relative volume of the 3D object  602 . 
     In some examples, the selectable location ( 732 ) may comprise specifying a location within the 3D object at which the embedded portion will be formed, and may be expressed via three-dimensional (x, y, z) coordinates of the boundaries of the embedded portion. In some such examples, the location of the embedded portion may be specified according to a selectable depth (parameter  733 ) below an exterior surface portion of the 3D object at which the first exterior surface portion (including an authentication surface feature) is targeted for appearance. One example illustrating such depth is shown in  FIG.  7 A  in which embedded portion  632  is shown being located at a depth D underlying first exterior surface portion  634 . It will be understood that the selected depth of the embedded portion (e.g.  632  in  FIG.  7 A ) will have an influence on type, size, intensity, etc. of the random characteristics of the first exterior surface portion (e.g.  634  in  FIG.  7 B ) including the authentication surface feature (e.g.  638  in  FIG.  7 B ) because of the random aspects of the thermal history of the first interior portion  630  ensuing after formation the embedded portion (e.g.  632 ). 
     In some examples, the random parameter  740  of the embedded portion engine  731  may be employed to introduce randomness into at least one of the location ( 732 ), volume ( 734 ), and/or shape ( 736 ) of the embedded portion (e.g.  632  in  FIG.  7 A ). In one aspect, employing such randomness in formation of the embedded portion (e.g.  632  in  FIG.  7 A ) may contribute to number, type, quality, etc. of random characteristics exhibited in a first exterior surface portion (e.g.  634  in  FIG.  7 B ) including an authentication surface feature (e.g.  638  in  FIG.  7 B ). In some examples, the random parameter  740  also may be employed to introduce randomness regarding a degree of fusion in association with fusion engine  750 , as further described below. 
     In some examples, in cooperation with the fluid dispenser engine  704 , the degree of fusion engine  750  (of thermal history engine  730 ) may be employed to control a degree of fusion for all of, or portions of, an embedded portion (e.g.  632  in  FIG.  7 A ) in order to influence a thermal history of a first interior portion (including embedded portion) underlying a first exterior surface portion (e.g.  634  in  FIG.  7 A,  7 B ) in order to influence appearance of the authentication surface feature (e.g.  638  in  FIG.  7 B ), such as its random characteristics. 
     In some examples, the degree of fusion engine  750  (of the thermal history engine  730 ) may provide control over a fusing agent parameter  752  and/or a detailing agent parameter  754 , which in turn control a volume and location at which a fusing agent and/or a detailing agent, respectively, are deposited onto a layer of build material. The relative volume of the fusing agent and/or detailing agent deposited to a particular voxel location (e.g.  274 ) determines a degree of fusion of the particular voxel location, as previously described in association with at least  FIG.  4   . In particular, in the absence of a fusing agent and/or detailing agent applied to a particular voxel location and upon application of radiation per energy source (e.g.  210  in  FIG.  4   ), no fusion will take place for the particular voxel location(s)  274  ( FIG.  4   ). This will result in unfused build material (i.e. free powder build material) at the particular voxel location(s)  274 . In some examples, the entire embedded portion (e.g.  632  in  FIG.  7 A ) may comprise unfused build material, which will affect the thermal history of additively formed layers overlying the embedded portion. On the other hand, upon depositing a selectable volume of fusing agent and/or detailing agent to a particular voxel location(s)  274 , one can control a degree of fusion of the build material at the particular voxel location(s)  274 . Via this arrangement, the particular voxel location(s)  274  may become at least partially fused and in some instances, fully fused. This arrangement also will affect the thermal history of additively formed layers overlying the embedded portion in a manner to produce different random characteristics of the overlying first surface exterior portion (e.g.  634  in  FIGS.  7 A,  7 B ) including an authentication surface feature (e.g.  638  in  FIG.  7 B ). 
     As further shown in  FIG.  9 A , in some examples, the degree of fusion engine  750  may be employed in association with the random parameter  740  of embedded portion engine  731  to introduce randomness into the volume, location, etc. of application of the fusing agent and/or detailing agent to thereby introduce randomness into the degree of fusion, in order to influence the thermal history of the first interior portion (e.g.  630 ), thereby contributing to the randomness of characteristics of the authentication surface feature (e.g.  638  in  FIG.  7 B ). 
     It will be understood that various functions and parameters of object formation engine  700  may be operated interdependently and/or in coordination with each other, in at least some examples. 
     In some examples, the object formation engine  700  comprises an authentication engine  770  to track and/or control at least an imager parameter  772  and a storage parameter  774 , which track and/or control an imager (e.g.  684  in  FIG.  8   ) and a data store (e.g.  682  in  FIG.  8   ), respectively, used to provide an authentication arrangement. In some such examples, the authentication engine  770  (including imager parameter  772  and storage parameter  774 ) may be implemented in a manner comprising at least some of substantially the same features and attributes as previously described in association with  FIG.  8   . 
       FIG.  9 B  is a block diagram schematically representing an example control portion  800 . In some examples, control portion  800  provides one example implementation of a control portion (e.g.  217  in  FIG.  4   ) forming a part of, implementing, and/or generally managing the example additive manufacturing devices, as well as the particular portions, components, material distributors, fluid supply, fluid dispensers, energy sources, control portion, instructions, engines, functions, parameters, and/or methods, as described throughout examples of the present disclosure in association with  FIGS.  1 - 8 B and  9 B- 10 B . In some examples, control portion  800  includes a controller  802  and a memory  810 . In general terms, controller  802  of control portion  800  comprises at least one processor  804  and associated memories. The controller  802  is electrically couplable to, and in communication with, memory  810  to generate control signals to direct operation of at least some the object formation devices, various portions and elements of the example additive manufacturing devices, as well as the particular portions, components, material distributors, fluid supply, fluid dispensers, energy sources, control portion, instructions, engines, functions, parameters, and/or methods, as described throughout examples of the present disclosure. In some examples, these generated control signals include, but are not limited to, employing instructions  811  stored in memory  810  to at least direct and manage additive manufacturing of 3D objects in the manner described in at least some examples of the present disclosure. In some instances, the controller  802  or control portion  800  may sometimes be referred to as being programmed to perform the above-identified actions, functions, etc. In some examples, at least some of the stored instructions  811  are implemented as a, or may be referred to as, a 3D print engine, an object formation engine, and the like, such as but not limited to the object formation engine  700  in  FIG.  9 A . 
     In response to or based upon commands received via a user interface (e.g. user interface  820  in  FIG.  9 C ) and/or via machine readable instructions, controller  802  generates control signals as described above in accordance with at least some of the examples of the present disclosure. In some examples, controller  802  is embodied in a general purpose computing device while in some examples, controller  802  is incorporated into or associated with at least some of the additive manufacturing devices, as well as the particular portions, components, material distributors, fluid supply, fluid dispensers, energy sources, control portion, instructions, engines, functions, parameters, and/or methods, etc. as described throughout examples of the present disclosure. 
     For purposes of this application, in reference to the controller  802 , the term “processor” shall mean a presently developed or future developed processor (or processing resources) that executes machine readable instructions contained in a memory or that includes circuitry to perform computations. In some examples, execution of the machine readable instructions, such as those provided via memory  810  of control portion  800  cause the processor to perform the above-identified actions, such as operating controller  802  to implement the formation of a 3D object with a particular thermal history to produce an authentication surface feature, as generally described in (or consistent with) at least some examples of the present disclosure. The machine readable instructions may be loaded in a random access memory (RAM) for execution by the processor from their stored location in a read only memory (ROM), a mass storage device, or some other persistent storage (e.g., non-transitory tangible medium or non-volatile tangible medium), as represented by memory  810 . The machine readable instructions may include a sequence of instructions, a processor-executable machine learning model, or the like. In some examples, memory  810  comprises a computer readable tangible medium providing non-volatile storage of the machine readable instructions executable by a process of controller  802 . In some examples, the computer readable tangible medium may sometimes be referred to as, and/or comprise at least a portion of, a computer program product. In other examples, hard wired circuitry may be used in place of or in combination with machine readable instructions to implement the functions described. For example, controller  802  may be embodied as part of at least one application-specific integrated circuit (ASIC), at least one field-programmable gate array (FPGA), and/or the like. In at least some examples, the controller  802  is not limited to any specific combination of hardware circuitry and machine readable instructions, nor limited to any particular source for the machine readable instructions executed by the controller  802 . 
     In some examples, control portion  800  may be entirely implemented within or by a stand-alone device. 
     In some examples, the control portion  800  may be partially implemented in one of the object formation devices and partially implemented in a computing resource separate from, and independent of, the object formation devices but in communication with the object formation devices. For instance, in some examples control portion  800  may be implemented via a server accessible via the cloud and/or other network pathways. In some examples, the control portion  800  may be distributed or apportioned among multiple devices or resources such as among a server, an object formation device, and/or a user interface. 
     In some examples, control portion  800  includes, and/or is in communication with, a user interface  820  as shown in  FIG.  9 C . In some examples, user interface  820  comprises a user interface or other display that provides for the simultaneous display, activation, and/or operation of at least some of the additive manufacturing devices, as well as the particular portions, components, material distributors, fluid supply, fluid dispensers, energy sources, control portion, instructions, engines, functions, parameters, and/or methods, etc., as described in association with  FIGS.  1 - 9 B and  10 A- 10 B . In some examples, at least some portions or aspects of the user interface  820  are provided via a graphical user interface (GUI), and may comprise a display  824  and input  822 . 
       FIG.  10 A  is a flow diagram of an example method  900 . In some examples, method  900  may be performed via at least some of the devices, components, material distributors, fluid supply, fluid dispensers, energy sources, instructions, control portions, engines, functions, parameters, and/or methods, etc. as previously described in association with at least  FIGS.  1 - 9 C . In some examples, method  900  may be performed via at least some of the devices, components, material distributors, fluid supply, fluid dispensers, energy sources, instructions, control portions, engines, functions, parameters, and/or methods, etc. other than those previously described in association with at least  FIGS.  1 - 9 C . 
     As shown at  902  in  FIG.  10 A , method  900  comprises additively manufacturing a 3D object including causing a first interior portion to experience a first thermal history selectably different from a second thermal history of at least second interior portions surrounding the first interior portion to include a first surface feature variation at a first exterior surface portion overlying the first interior portion, the first exterior surface portion being different in appearance than a second exterior surface portion overlying the second interior portions. As further shown at  904 , method  900  comprises optically recording, and storing in memory, an image of at least one of: the first surface feature variation of the first exterior surface portion; and the second exterior surface portion. 
     In some examples, the method  900  may further comprise determining, at a later time, authenticity of a candidate 3D object by comparing at least one of: the stored image of the first surface feature variation at the first surface exterior portion with a corresponding first surface exterior portion of the candidate 3D object; and the stored image of the second exterior surface portion with a corresponding second exterior surface portion of the candidate 3D object. In some such examples, such determination may be implemented via the authentication engine  770  described in association with at least  FIG.  9 A  and/or in accordance with at least some of substantially the same features and attributes of the example described in association with at least  FIG.  8   . 
     In some examples, the first surface feature variation may sometimes be referred to as an authentication surface feature, an authentication surface mark, an authentication surface colorization, etc. in the manner previously described throughout examples of the present disclosure. 
     Although specific examples have been illustrated and described herein, a variety of alternate and/or equivalent implementations may be substituted for the specific examples shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific examples discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.