(1) A German invention has for its object the rendering more or less transparent of paper used for writing or drawing, either with ink, pencil, or crayon, and also to give the paper such a surface that such writing or drawing may be completely removed by washing, without in any way injuring the paper. The object of making the paper translucent is that when used in schools the scholars can trace the copy, and thus become proficient in the formation of letters without the explanations usually necessary; and it may also be used in any place where tracings may be required, as by laying the paper ov«r the object to be copied it can be plainly seen. Writing-paper is used by preference, its preparation consisting in first saturating it with benzine, and then immediately coating the paper with a suitable rapidly-drying varnish before the benzine can evaporate. The application of varnish is by preference made by plunging the paper into a bath of it, but it may be applied with a brush or sponge. The varnish is prepared of the following ingredients: - Boiled bleached linseed-oil, 20 lb.; lead shavings, 1 lb.; oxide of zinc, 5 lb.; Venetian turpentine, 1/2 lb. Mix and boil 8 hours.
After cooling, strain, and add 5 lb. white copal and 1/2 lb. sand-arach. (2) The following is a capital method of preparing tracing-paper for architectural or engineering tracings: - Take common tissue or cap-paper, any size of sheet; lay each sheet on a flat surface, and sponge over (one side) with the following, taking care not to miss any part of the surface: - Canada balsam, 2 pints; spirits of turpentine, 3 pints; to which add a few drops of old nut-oil; a sponge is the best instrument for applying the mixture, which should be used warm. As each sheet is prepared, it should be hung up to dry over two cords stretched tightly and parallel, about 8 in. apart, to prevent the lower edges of the paper from coming in contact. As soon as dry, the sheets should be carefully rolled on straight and smooth wooden rollers covered with paper, about 2 in. in diameter. The sheets will be dry when no stickiness can be felt. A little practice will enable anyone to make good tracing-paper in this way at a moderate rate. The composition gives substance to the tissue-paper. (3) You may make paper sufficiently transparent for tracing by saturating it with spirits of turpentine or benzoline.
As long as the paper continues to be moistened with either of these, you can carry on your tracing; when the spirit has evaporated, the paper will be opaque. Ink or water-colours may be used on the surface without running. (4) A convenient method for rendering ordinary drawing-paper transparent for the purpose of making tracings, and of removing its transparency, so as to restore its former appearance when the drawing is completed, has been invented by Puscher. It consists in dissolving a given quantity of castor-oil in one, two, or three volumes of absolute alcohol, according to the thickness of the paper, and applying it by means of a sponge. The alcohol evaporates in a few minutes, and the tracing-paper is dry and ready for immediate use. The drawing or tracing can be made either with lead-pencil or Indian ink, and the oil removed from the paper by immersing it in absolute alcohol, thus restoring its original opacity. The alcohol employed in removing the oil is, of course, preserved for diluting the oil used in preparing the next sheet. (5) Put 1/4 oz. gum-mastic into a bottle holding 6 oz. best spirits of turpentine, shaking it up day by day; when thoroughly dissolved, it is ready for use. It can be made thinner at any time by adding more turps.
Then take some sheets of the best quality tissue-paper, open them, and apply the. mixture with a broad brush. Hang up to dry. (6) Carbon tracing-paper is prepared by rubbing into a suitable tissue a mixture of 6 parts lard, 1 of beeswax, and sufficient fine lampblack to give it a good colour. The mixture should be warm, and not be applied in excess. (7) Saturate ordinary writing paper with petroleum, and wipe the surface dry. (8) Lay a sheet of fine white wore tissue-paper on a clean board, brush it softly on both sides with a solution of beeswax in spirits of turpentine (say about 1/2 oz. in 1/2 pint), and hang to dry for a few days out of the dust.