The invention is directed to a technique for the generation of film negatives which will be used in a chemical etching process to provide a previously etched surface with texturing on the broad, flat areas of a previously etched surface. A rubbing is used to form a basis for a series of photographic negatives which provide an indication of the different levels of texturing.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention is directed to a technique for reproducing a model surface by 
chemical etching onto an embossing plate; and, more particularly, the 
invention is directed to a technique for forming negatives of the texture 
of the surfaces of the model surface. 
2. Description of the Prior Art 
U.S. Pat. No. 3,907,622 teaches a technique for producing a 
three-dimensional effect in metal by the use of a series of photographs 
wit chemical etching. The invention herein is a technique for providing 
the product formed by that patent with surface texturing on the flat and 
smooth areas of the previously etched metal surface. 
SUMMARY OF THE INVENTION 
The invention is directed to a method for forming a three-dimensional 
surface wherein the initial three-dimensional surface has been formed in a 
series of steps using a conventional chemical etching process wherein a 
plurality of photographs of a model are sequentially exposed to a 
plurality of resist coatings to form the general shape of the 
three-dimensional configuration of the model in a series of steps. The 
above is accomplished by using the teaching of U.S. Pat. No. 3,907,622. 
The improvement over that patent is the making of a rubbing of the surface 
of the model, whereby the rubbing forms a reproduction of the surface 
contour of the model with the different levels of the contour of the model 
being represented by a various tones of a single color. A series of 
photographic negatives are made of this rubbing so that the different 
tones of color will be reproduced in the negatives to show the different 
levels of texture for the model. The second set of negatives are then used 
very much in the same manner as the first set of negatives with a series 
of resist coatings applied to the previously etched step-like etched 
surface to provide said step-like etched surface with a texturing 
primarily of the flat areas of the etched surface. 
This, then, converts the metal surface made by the technique of U.S. Pat. 
No. 3,907,622 from a step-like reproduction of the model to almost a 
mirror-like reproduction of the model surface.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The initial embossed metal surface is made according to the technique of 
U.S. Pat. No. 3,907,622, and this, then, provides a surface such as that 
shown in FIG. 1. It can be seen that the surface of FIG. 1 has a large 
number of flat areas. These flat areas must be provided with some type of 
texturing so that the metal surface will more nearly simulate the actual 
model being produced. The model being produced does not have its contour 
as a series of steps but as a series of curved lines. 
The model is taken and on the surface thereof there is placed first a 
carbon paper and then a tracing paper though one could carry out the 
invention by simply using a tracing paper along. With the paper now 
positioned on the surface of the model, a pencil or some other object is 
rubbed across the surface of the model. The pencil alone will operate with 
the single piece of paper, and any type of pointed instrument can be used 
when the carbon paper and transfer paper are used together. Rubbing across 
the surface of the model with the paper thereon will produce a rubbing of 
the surface of the model. As is well known in the art, a rubbing is a 
reproduction of the surface of the irregular object with the texture or 
various levels of the surface being shown as different tones of the same 
color. For example, when the pencil rubbing is made of a three-dimensional 
surface, the high areas show up as being a dark color while the low areas 
appear as a light color. 
After the rubbing of the model surface is made, the image of the rubbing is 
then photographed using high-contrast lithographic film to create an 
etching film duplicate of the rubbing. Various exposure times are employed 
while keeping the F-stop constant during photographing. In this manner, a 
series of films representing the existing levels of texture of the model 
can be generated for etching purposes. These films may be used as is or 
may be retouched to alter certain features of the model to make a more 
pleasing reproduction. Also the total negative may be used or only 
selected portions thereof. 
In one specific example of the invention, high-contrast lithographic film 
sold by Kodak as "Kodalith Ortho Filmtype 3 #6656" film is used with an 
F-11 stop and the following exposure times: 9, 14, and 17 seconds to 
provide three texture films. At the 9 second exposure time, the negative 
formed from the film will show only the very dark areas of the rubbing and 
at the 17 second exposure time, the negative of the film generated will 
show both the dark and medium tone of the rubbing. These negatives are 
then superimposed upon the step-like etched surface prepared according to 
U.S. Pat No. 3,907,622; and utilizing the resist and negative technique of 
that patent, a series of surface coatings are prepared for chemical 
etching and are chemically etched. This, then, converts the embossing 
plate configuration of FIG. 1 into that of FIG. 2 wherein the broad, flat 
areas are now provided with a texturing. In effect, the texturing 
technique herein converts the step-like sharp shoulder configuration of 
FIG. 1 into a curve surface configuration which more closely represents 
the true surface of the model being used. 
The invention herein basically is the forming of a series of step-like 
impressions of the different levels of the irregular surface and then 
using a second set of photographing negatives to provide texturing to the 
flat surfaces of the different flat areas of the previously formed 
step-like pattern.