The most useful dyes for this purpose are the Sulphur dyes, which, as the student will remember, can be applied in the cold, with very short exposure to the dye-liquor, and are fixed firmly by exposure to the air, giving results fast to light and extremely fast to washing. A paste made from wheat flour, thickened a little with an inert powder, like powdered chalk or zinc oxide, will work fairly well, acting as a purely mechanical protection to the fibre. But much better results can be obtained by adding to the paste as much as it will absorb of the easily soluble chemical, zinc sulphate, which acts chemically in resisting the action of these particular dyestuffs. The Sulphur colors, as before explained, are kept in solution in the dye-bath, by the presence of sodium sulphide, and when this is absent or is destroyed by any cause, the dyestuff is precipitated as an insoluble, inert powder. Now, when zinc sulphate comes in contact with sodium sulphide it at once decomposes the latter, forming a white precipitate, zinc sulphide, which has no action at all on either dyestuff or cloth. Accordingly a paste containing zinc sulphate has far greater efficiency as a resist than any mixture that acts purely mechanically. Resist stencil pastes can be obtained, in tubes, at moderate prices, but can also be readily prepared by making not too stiff a paste, with wheat flour thoroughly boiled with a saturated solution of zinc sulphate instead of with water, and then stirring into this paste some powdered chalk or zinc oxide, until of the proper consistency for stencilling. To use this paste, the cloth, as usual, should be washed free from dressing, and after being smoothed with a hot iron, should be slightly dampened. The paste is then brushed through the stencil on to, and into, the cloth, which is then allowed to dry. The dye-bath should then be prepared of Sulphur dyes carefully dissolved, in a separate cup or saucepan, in a hot solution of sodium sulphide and sodium carbonate (soda), and added to cold water in the dye-bath. A few drops of “Turkey red oil” added to the dye-bath helps to prevent a thick scum from forming on top of the liquor, while the addition of a tablespoonful of salt dissolved in a little hot water helps the rapidity and depth of the dyeing. Plenty of color should be used excepting for very light shades, for the dyeing should be done just as quickly as possible. For silk some syrup should be added. The stencilled cloth is then quickly moistened in cold water, placed in the dye-bath, kept there two or three minutes, below the level of the liquid; it is then taken out, the liquor drained off, and after a minute or two, wrung off; the cloth is then shaken out, and exposed to the air, for some ten minutes, to set the color. After this it is well washed in a boiling soap bath, and, as the paste washes out, the stencilled pattern will show light against the dark background.