Posted by Patrick Mackle on January 30, 2003
Mike Jackson - Patent # 494,999While we are on the subject of chipping I would like to say-
Rick rediscovered that method of using asphaltum as an aid for chipping, coupled with those cool old reuseble acid etched zinc sandblast templates. The glass was coated with asphaltum and the zinc templates were placed against the glass and the sand would pass through the template efficiently removing the tar and frosting the areas to be chipped whilest the remaining tar was smartly left to retain the glue. Later in
eliminating the zinc stencil, he acquired the plotter which he used to protect the asphaltum.
Now, I can't help but think that Rawson & Evans used the zinc method for their production pieces to save time, but I can't see them using large amounts of asphaltum to chip their larger pieces. This thought has always been in my mind since I had the opportunity to talk to a lady whose husband's father worked for R&E.
She told me about the gluechipping they used to do and mentioned that they would "break the glue's back".
That term stuck in my brain even though at the time I wasn't really interested in sandblasting or chipping, I really wanted to know about acid etching.
Recently in doing alot of trial gluechipping I remem-bered that term. I have always placed my panels into a refrigerator to chill the glue, cut and peel the edges to get a perfect edge. You see that by doing this it gives you a perfectly straight edge, and as the glue dries that edge shrinks inward, creating a fine tapered bevel. The significance of this bevel is that the glue is now thinner right along the leading edge of the glue. Kind of like setting a "backfire" the glue begins to pull into itself, lessening the chance of it running a chip into the clear glass. I believe R&E knew this and thus were able to hold their line quality so well.
Now, I Know they didn't use a refrigerator, so I thought, how did they do it. When I cut the glue after it gelled, it healed right back together, I couldn't find the cut.
The other night it hit me to wait until the glue dried, nearly before it would be too dry to cut easily.
The result was amazing, the cut glue split apart so significantly
as it dried that it nearly seperated into a perfect "V".
This was done without asphaltum and with a 4 mil sandblast mask left on the glass, ready for a second chip. I remember Rick saying that the mask should be removed or it would interfere with the chips, which it would do unless the glue is cut. I left the mask on and used it as a guide to cut. R&E didn't have masking back then, they probably used glue and varnished paper.
They probably flowed the glue over entire letters or words, then cutting against the edge of the paper "broke the glue's back" on the seperate letters.
Anyone's thoughts are welcome.
Pat
Hi Pat,
I scrolled down to a post I made on Nov. 9, 03 and found some slightly related information. The game with a patent is to give enough information to the patent office to convince them your new idea or process if different, yet not telling too much to you competitor. Something tells me they conveniently failed to mention the step about cutting the glue at the point when it would have stopped re-healing. I pasted in a couple of paragraphs below from my Nov. post.
"According to Samuel Evans patent, for the stencil in this process, he used heavy document manila paper, soaked in oil and let dry. The pattern material could be stacked and cut in groups of 8 to 20 stencils at on time us a sharp knife. This was done off the glass. The glass was cleaned, then coated with a layer of soap solution (one variant of the process calls for an under layer of asphaltum) and the stencil material was applied over it. The panel was then frosted with a sandblaster. According to the patent info, the warm glue was brushed onto the panel.
Now, the interesting part. While the glue was still very soft, they quickly pulled the manila pattern off the glass, leaving only glue in the frosted areas. I've never really tried that exactly, but in the Bob Mitchell process, you had to hand cut around all edges and remove the stencil. It is similar but Rawson and Evans didn't have adhesive stencil. The patent uses the work "quickly" a couple of times...so maybe there is something related to the speed they pulled the paper, or maybe that is related to the timing after the glue was applied."
If you only read these two paragraphs, you might assume they simply yanked the stencil up and it would cut at the manila paper lines. If so, you'd have to do it while the glue was still quite soft. If "breaking the back" of the glue, you'd have to wait until it almost dried as Pat said.
I've never thought it would have been to practical to have vats of mineral spirits large enough to emmerse huge pieces of glass, even though the patent above mentions it as one of the techniques.
There is some very intresting information surfacing here and now. There were probably numerous techniques used, depending on the size, complexity and whether it was to be repeated.
Mike Jackson
Denver Chapter of the Letterheads