# The Additive Manufacturing of Glass: A Critical Review
## 2 Glass AM Techniques
### Synopsis of Reported Glass AM Methods  
The following three tables (Tables 1-3) provide insight into the glass AM methods presently reported in the literature and relevant patents, along with their key characteristics in synopsis.  
Figure 13: Diagram and model photographs demonstrating the major methods of binder-based AM. (**a**) A typical direct ink writing process. The object is printed (scale bar: 0.5 mm), a green object is produced, the object is dried and binders are removed (scale bar: 5 mm), and the remaining glass feedstock is consolidated into a solid object [54]. (**b**) A typical light-based process. A glass feedstock is added to a suitable photopolymer binder. An existing method of AM applies a light source to cure the photopolymer in the desired shape. Temperature and/or chemical means are used to remove the binder and consolidate the feedstock into a solid glass object [52].  
\begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline
**Method** & **Feed Material** & \begin{tabular}{c} **Deposition** \\ **Width Scale** \\ **(ima)** \\ \end{tabular} & \begin{tabular}{c} **Length Scale** \\ **(mm)** \\ \end{tabular} & **Advantages** & **Limitations** & **Related Literature** \\ \hline \multirow{4}{*}{\begin{tabular}{l} Directed Energy \\ Deposition \\ \end{tabular} } & \begin{tabular}{c} Soda-Line \\ Filament/Vowder \\ \end{tabular} & -0.1-4 & -1-200 & \begin{tabular}{c} Excellent material fusion \\ Excellent optical clarity \\ \end{tabular} & \begin{tabular}{c} \(\star\) \\ Excellent optical clarity \\ \end{tabular} & \
\begin{tabular}{c} Lacks fine detail due to \\ melting behaviour \\ Feed mechanism needs consideration \\ for uninterrupted printing \\ \end{tabular} &
\begin{tabular}{c} [12, 13, 14, 27, 33, 34, 35, 36, 37, 38, 40, 38, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 5  
\begin{table}
\begin{tabular}{l l l l l} \hline \hline
**Binder-Based AM Method** & **Feedstock Material** & **Deposition Width Scale (mm)** & **Length Scale (mm)** & **Related Literature** \\ \hline Fused Deposition Modelling & Silica particles + Thermoplastic & –0.4 & –1–200 & –1–200 \\  & polymer binder & (Polymer printing) & (Polymer printing) & [53] \\ \hline Direct Ink Writing & Colloid of silica-based glass feedstock, rheological agents + Solvent & –0.1–1 & –1–200 & [51, 54, 69, 70, 71] \\ \hline Light-Based & & & & \\ (Steroolithography, Two-Photon & Silica particles + Photopolymer binder & –0.0001–0.1 & –1–200 & [52, 55, 56, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84] \\ Polymerisation, Direct Laser Writing, etc.) & & & \\ \hline \hline \end{tabular}
\end{table}
Table 2: Synopsis of binder-based glass AM methods.  
\begin{table}
\begin{tabular}{l l l l} \hline \hline
**Patent Name** & **Date** & **Assignee** & **Patent Number** & **Ref.** \\  & **First Filed** & **Assignee** & **\%****Fact Number** & **Ref.** \\ \hline Methods and apparatus for additive manufacturing of glass & 2015 & Massachusetts Institute of Technology & US10266442B2 & [85] \\ \hline A kind of 3D printing equipment for chalcogenide glass element & 2016 & China Building Materials Academy & CN106116120A & [86] \\ \hline Additive manufacturing systems and method for making glass articles & 2017 & Corning Incorporated & US20210101818A1 & [87] \\ \hline
3D printing system for printing high melting temperature materials & 2018 & Micron 3 Dp Ltd., D Swarovski KG & WO2018163006A1 & [88] \\  & & (Location depending) & & \\ \hline Three-dimensional printing system & 2020 & Maple Glass Printing Pty. Ltd. & AU2021289614A1 & [89] \\ \hline \hline \end{tabular}
\end{table}
Table 3: A snapshot of patents related to glass AM, confined to those that employ solid-state glass processing (i.e., glass in the semi-solid/viscous state) methods.