This section is from the "Henley's Twentieth Century Formulas Recipes Processes" encyclopedia, by Norman W. Henley and others.
Inks made with nut-galls and copperas can be removed by using a moderately concentrated solution of oxalic acid, followed by use of pure water and frequent drying with clean blotting paper. Most other black inks are erased by use of a weak solution of chlorinated lime, followed by dilute acetic acid and water, with frequent drying with blotters. Malachite green ink is bleached by ammonia water; silver inks by potassium cyanide or sodium hyposulphite. Some aniline colors are easily removed by alcohol, and nearly all by chlorinated lime, followed by diluted acetic acid or vinegar. In all cases apply the substances with camel's-hair brushes or feathers, and allow them to remain no longer than necessary, after which rinse well with water and dry with blotting paper.
Citric acid.......... 1 part
Water, distilled...... 10 parts
Concentrated solution of borax.......... 2 parts
Dissolve the citric acid in the water and add the borax. Apply to the paper with a delicate camel's-hair pencil, removing any excess of water with a blotter. A mixture of oxalic, citric, and tartaric acids, in equal parts, dissolved in just enough water to give a clean solution, acts energetically on most inks.
Alum, 1 part; amber, 1 part; sulphur, 1 part; saltpeter, 1 part. Mix well together and keep in a glass bottle. If a little of this powder is placed on an ink spot or fresh writing, rubbing very lightly with a clean linen rag, the spot or the writing will disappear at once.