SPECIAL INKS Sympathetic Inks.—These inks are invisible until brought out by the ef fect of heat or some chemical. For an invisible ink, write with fresh milk, which will not show until the paper is gently heated.
Or write with a solution of sugar in water.
Or write with a mixture .of 1 part of sulphuric acid and 20 parts of water, using a quill or gold pen. The acid will corrode an iron or steel pen. This is invisible until the paper is made warm enough to evaporate the water, when the acid will char the paper in black characters.
Or write with a solution of acetate of lead, and afterwards expose the writing to the fumes of a brimstone match.
Or write with a weak solution of nutgalls, and apply a solution of iron to the paper.
Or write with a solution of nitrate of silver, and apply a solution of com mon salt. These methods have often been used to conceal subjects of cor respondence by writing letters with ordinary inks, and between the lines writing with invisible ink another mes sage. The secret of the combination must, of course, be known to the per son for whom the writing is intended.
Luminous Ink. — Dissolve 1 dram of phosphorus, in 1 ounce of oil of cinnamon. Cork tightly, and put the bottle in hot water until dissolved. Letters written with this solution will be visible in the dark.
Hectograph Ink.—Mix 1 ounce of iodine-green or methyl-violet aniline colors with 1 ounce of glycerin, and dissolve the mixture in 10 ounces of distilled water. This is used in print ing from a gelatin pad, usually called a hectograph. To make such a pad, cover 1 ounce of gelatin with cold water, and let stand over night. Put in a new tin dripping pan or other tin dish having low sides and square corners 121 ounces of gelatin, and heat slowly, but do not let it boil. Stir in the soaked gelatin and let the mix ture stand over a slow fire until the water is all evaporated. This will produce a solid pad of clear gelatin. Cover from dust and let stand over night. To use this pad, write with the above ink, let the ink dry, and moisten the pad slightly with water by means of a brush. When the pad
is nearly dry, lay the writing, face down, on the pad, rubbing it down gently with a soft cloth. Let it stand a minute or more according to the number of copies required, remove the paper, and the pad is ready to print from. Use for this purpose soft unsized paper. Lay the paper on the pad, smoothing it with a cloth or roller, and remove immediately. Con tinue to take copies until the ink is exhausted. Then wash the pad with cold water and a sponge to remove the surplus ink. When dry, it is ready to be used again as before.
Rubber-stamp Ink. — Inking pads for rubber stamps may be re-inked by means of aniline dyes of suitable color mixed to the consistency of thin cream with glycerin.
Metal-label Ink.—Dissolve 1 ounce of copper in 10 ounces of nitric acid, and thin with 10 ounces of water.
Or mix 2 ounces of powdered sul phate of copper, 1 ounce of powdered sal ammoniac, and 4 ounces of acetic acid. Stir in lampblack or other pigment of any color desired.
Or dissolve equal quantities of ver digris and sal ammoniac in water, and add lampblack or other pigment to color. Mix the ingredients in earth enware with wooden paddles, as they will corrode metals. They are suit able for writing on steel, tin plate, or sheet zinc.
Mix 1 ounce of muriatic acid and ounce of nitric acid. Cover the metal surface with beeswax, and when cold, write on it with any sharp-point ed instrument that will cut through to tht wax. Apply the mixture with a small brush or feather, and let it lie for a few minutes according to the depth of etching desired. Then rinse off the wax and acid in hot water. Either of the acids alone will cut iron or steel, but the mixture is required for gold or silver. After rinsing off the acids, apply a little sweet oil or olive oil. The smoothness of the etch ing will depend upon the cleanness with which the wax is cut and re moved from the metal in each let ter. Hence a sharp-edged tool is the best.