Etching Processes
by Phyllis Hayes
Issue No. 95 - March 1981
(Editor's Note: The following article was prepared for the November 1980 Study Group meeting of The Michigan Caprices. We thank them for sharing this information with us.)
The more we learn about the particular Cambridge we are collecting, the more we treasure each piece we have and admire those who had a hand in making it into such a beautiful piece of glass. Many who have visited the Bennett Museum and read past articles of the Crystal Ball have somewhat of an idea as to how plate etching was done to make Rosepoint and Cambridge's other beautiful etchings. However, I would like to review this procedure first. Thanks to an article done by Charles Upton on an interview with Virgil Saltz, a former employee of the Cambridge plant, there is a lot more information that I was not aware of. (Crystal Ball #23)
The etching process started with a plate that was metal. The background of this plate was etched away so the main design area appeared in raised relief. Of course several different plates of the same pattern had to be made to fit the different size articles being made.
The etching ground, which consisted of beeswax, lampblack, resin and turpentine, was cooked at least over night before being used. The etching ground was then deposited into the low areas of the plate and the higher pattern areas were scraped clean.
A special type of transfer paper was then cut to proper size and applied to the wax covered plate. A piece of felt would be used to rub the paper and cause it to adhere to the wax. Keeping the plates slightly warm permitted the wax to be lifted from the plate along with the transfer paper.
The transfer was now ready to be applied to the blank. It was covered with wax in all of the areas of the background and the lines that made up the design of the pattern were clean of any wax. It was then applied in the proper position to the blank and again rubbed gently with felt, which caused it to adhere to the glass. This step was repeated over and over until the blank was decorated with the required amount of design.
The blank was then immersed in a solution of alcohol and water. This permitted the removal of the paper from the wax and thus completed the actual pattern transfer operation. The blank was then sent to a "paint girl" who would cover all of the remaining exposed areas of the glass. This was done entirely by hand, using a small paintbrush and working from a heated pot of etching ground.
As many as two dozen articles, depending upon their size, would then be stuck to a wax covered board approximately 18 by 24 inches. This board was then inverted and immersed in a tank of acid. Hydrofluoric acid was used and it was controlled at a constant temperature. The etching process required between three and eight minutes. This was controlled by the acid's strength and the desired depth of the pattern being etched.
Upon being removed from the acid, the article would be placed in the "scalder". This was a machine that used a combination of hot water and steam to remove the etching ground from the article. During this procedure the wax would be carried by the water into a tank built into the base of the machine. Here the wax would float enabling the workers to skim it off for reuse.
The article of glass which started out as a plain blank has now been etched with a pattern and has had the wax removed from it. The final etching process occurred on the saw dust table. Here the article was dried, cleaned and polished by a brisk rubdown of sawdust. If the article were to receive no further decoration it would be wrapped in tissue and placed in a storage bin. It would later be sent to the packing room where it would be carefully packed for shipment.
From the section in the book "Glass in the Modern World" by F.J. Terrance Nialone, I found several other methods used in decorating glass, that I'm sure were very similar to the methods Cambridge used in the past.
Needle Etching: The blank to be decorated is given a coating of a resist such as beeswax, paraffin or resin and the required pattern is scratched on with a steel needle. The article is then immersed in hydrofluoric acid solution for about ten minutes. Warm water is used to remove both resist and solution. Glass can also be given a white finish by the application of ammonia bifluoride mixtures. Sometimes the article would then be spray rinsed with a more dilute mixture that smoothes the surface left by the first etching. Of course I'm sure if only a portion of the blank was to be etched, it must have been covered with a wax in the areas that the etching was not desired. Ammonium bifluoride is used in the ink for drawing designs in glass.
Sand Blasting: This is an inexpensive method of making glass translucent by bombarding it by means of compressed air, with course round grained sand. Patterns can be achieved by masking parts of the surface with a soft rubber stencil. The effect produced, though rougher than that obtained by grinding, is adequate for inexpensive mass-produced glassware.
Cutting or Grinding: The lead-crystal glassware intended for cutting is made strong and heavy to allow the deep cutting that refracts light and shows up prismatic patterns. The decoration is first inked onto the article as a guide and the design cut by a slowly revolving wheel of sandstone or carborundum, using water for cooling and removing the waste. There are three basic types of cut: hollow cut, made by a convex wheel; a bevel cut, which is V-shaped; and a panel cut, which is flat. The rough white surface left by cutting is removed either by hydrofluoric acid etching or by polishing on felt wheels with a fine abrasive.
Copper-wheel engraving, which produces shallower cuts, is more suitable for decorating lighter, thinner glassware. Linseed oil mixed with emery powder or carborundum is fed onto a revolving copper wheel to provide an abrasive. So precise are the results obtained by this method that to produce a fairly simple design an engraver may use as many as 50 wheels ranging in diameter from 3 mm to 10 cm.
Other effects: A wide range of both transparent and opaque colors may be applied to the glass surface. When fired in special decorating lehrs, they become reasonably permanent. Many of these are applied by painting the article with an organic metallic compound that, after firing, leaves an extremely thin film of the metal on the surface of the glass. An alternative method is to apply an inorganic oxide colorant to some organic vehicle that will disappear during firing. A third method is enameling. The enamels used generally consist of low melting point glasses. These are applied by sprinkling or dusting them in fine powder form onto a surface that has previously been given a light coating of gum.
With the quality of glass, the special etchings and the workmanship that went into Cambridge Glass, it's no wonder we all feel it is one of the most beautiful ever made.