Polychrome as recalled by Mr. Robert Gumbinner...2 Stencil Manufacturing 1

Polychrome’s original business was in stencil. Here Mr. Gumbinner recalls early days of stencil manufacturing.

Stencil Manufacturing: (part 1)

Mimeograph stencils are made by coating a porous tissue sheet with a highly oil-loaded nitro-cellulose solution. When I started with Polychrome, a sheet of Yoshino tissue (hand made paper) from the bark of a type of Mulberry tree had been used. These sheets were mounted on a bar and carried by a conveyor chain through a drying tunnel. By this time the C H Dexter company, which was making tea bag, developed a Fourdinier paper making machine in which the Fourdinier wire instead of being horizontal was at an uphill

angle. In this way they were able to obtain squareage. That is, the fibers were dispersed in all directions. This was necessary for a stencil otherwise letters like “O” would chop out. Later we improved our stencils by having Dexter add a wet strength resin to the sheet. Since the stencil tissue was now available in rolls, we designed a method of distributing the heated drying air through a plenum to support the coated sheet. The stencil tissue in passing over the coating roll picked up five times its weight of the wet coating solution needed considerable support.

When I came on board, Polychrome was getting many complaints about the performance of their stencils. One month, more stencils than we made were returned including stencils made by other manufacturers. I worked on improving the stencil solution formula, which was basically eight parts of oil to one part of nitrocellulose plus pigments. I balanced the oils to about equal parts of oleic acid, ocenol (oleic alcohol from whale oil), and butyl stearate. We also included about 2 parts of castor oil plus the castor oil into which the pigments were ground. Castor oil was a plasticizer for nitrocellulose. Also included was halowax, and a long chain amide to prevent the stencils from sticking together and a preserv­ative. The pigment was initially iron blue for the standard blue stencil. Later we change to phthalo­cyanine blue. Chrome yellow was used for yellow stencils, titanium dioxide for white and phthalocyanine green for green stencils.