Finely-powdered nut-galls 10 oz., sulphate of zinc (powdered) 2 oz., sulphate of iron (powdered) 4 oz., gum-arabic (powdered) 1 oz.; 1 oz. of this powder when finely sifted, added to about 1/2 pint of water and well shaken, will form a good ink.
If a forger has used a different ink to that used by the original writer of the document, his error can be made manifest in the following manner: - Get 9 1/2-oz. or 1-oz. vials, and fill separately with (1) dilute sulphuric acid; (2) concentrated muriatic acid; (3) dilute nitric acid; (4) solution of sulphurous acid; (5) solution of caustic soda; (6) concentrated solution of oxalic acid; (7) solution of chloride of lime; (8) solution of tin crystals; (9) solution of photo-chloride of tin. Take nine quill pens, each one for its particular reagent. Now, with a rule, draw lines crossing original and suspected portions; the difference will show itself at a glance. (Chem. Rev.)
If the ink is prepared with a certain proportion of gelatine, the addition of a little bichromate of potash, followed by exposure to sunlight, has been recommended for rendering the ink so insoluble in water that it will not run or spread when water-colours are used for shading the sides of the lines.
In order to restore faded ink all that is necessary is to moisten the paper with water and brush over the writing with a solution of sulphide of ammonium. The ink will become black immediately, from the formation of the black sulphide of iron. Of course this means of restoration is not applicable with aniline inks. (Boston Jl. Chem.)
A good ink eraser is "thus made: Take 1 lb. chloride of lime, thoroughly pulverised, and 4 qt. soft water. The above must be thoroughly shaken when first put together. It is required to stand 24 hours to dissolve the chloride of lime; then strain through a cotton cloth, after which add a teaspoonful of acetic acid to every ounce of the chloride of lime water. The eraser is used by reversing the penholder into the fluid, and applying it, without rubbing, to the word, figure, or blot required to be erased. When the ink has disappeared, absorb the fluid with a blotter, and the paper is immediately ready to write upon again. Chloride of lime has before been used with acids for the purpose as above proposed; but in all previous processes the chloride of lime has been mixed with acids that burn and destroy the paper.