Varnish the cloth with Canada balsam dissolved in turpentine, to which may be added a few drops of castor-oil, but do not add too much, or it will not dry. Try a little piece first with a small quantity of varnish. The kind of cloth to use is fine linen; do not let the varnish be too thick. Sometimes difficulties are encountered in tracing upon cloth or calico, especially in making it take the ink. In the first place, the tracing should be made in a warm room, or the cloth will expand and become flabby. The excess of glaze may be removed by rubbing the surface with a chamois leather, on which a little powdered chalk has been strewn; but this practice possesses the disadvantage of thickening the ink, besides, it might be added, of making scratches which detract from the effect of the tracing. The use of ox-gall, which makes the ink " take," has also the disadvantage of frequently making it "run," while it also changes the tint of the colours. The following is the process recommended: Ox-gall is filtered through a filter paper arranged over a funnel, boiled, and strained through fine linen, which arrests the scum and other impurities. It is then placed again on the fire, and powdered chalk is added.

When the effervescence ceases, the mixture is again filtered, affording a bright colourless liquid, if the operation has been carefully performed. A drop or two may be mixed with the Indian ink. It also has the property of effacing lead-pencil marks. When the cloth tracings have to be heliographed, raw sienna is also added to the ink, as this colour unites with it most intimately, besides intercepting the greatest amount of light.