WARNERKE'S PROCESS. —A simplified collotype process, invented by M. Raymond, of Paris, and introduced in this country by Warnerke. The printing surface employed is vegetable parchment, coated with a suitable gelatine. This is sensitized in a bichromate bath, and then squeegeed on to a talced glass. When dry, it can be stripped from the glass, and is ready for printing from, under a reversed negative, the exposure being prolonged " until the details cor responding with the most opaque parts of the negative are discernible." The time required varies, of course, with the actinicity of the light and the density of the negative. After exposure beneath the negative the par,thment is removed, and the back of it exposed a second time for about five minutes in order to more firmly fix the gelatine film to the parchment and to diminish the swelling of the gelatine, and consequently the relief. The next operation is to wash the bichromate from the film in several changes of water ; it is then blotted and hung up to dry. The dry film is immersed in water for about half an hour, the superfluous moisture blotted off, and the parchment stretched over a wooden frame. The apparatus for holding the parchment consists of solid wooden board as a base. and a clamping frame. After it is stretched on the frame the wooden block, which is smaller but thicker than the frame, is placed under it, and the frame lowered. The block being thicker raises the parchment, and renders it perfectly and
The gelatine surface is then covered for an hour with a solution of Water to ounces Glycerine 24 ounces Ammonia i ounce This renders the gelatine better permeable to moisture, and causes it to repel the print ing ink.
After about an hour the glycerine solution remaining on the surface is blotted off with a soft rag dabber, and it is ready tor printing from.
A good collotype ink is required this is spread evenly over the surface with a glue roller, a sheet of paper laid on it, and this backed with a piece of stout, but fine, felt, and the whole placed under a press. An ordinary letter-copying press answers the purpose. Pressure is applied and re moved, and then the paper will be found to have received an impres sion of the collographic plate. For clean margins, slips of oiled paper or cut-out masks should be laid on the printing surface before the paper is applied. After about three or four dozen impressions have been taken off, the plate is re moistened with a solution of gly cerine and water.