By means of water one can discover what acids, alkalis, or salts the parts of the paper with colored borders or white spots contain.

With the aid of a pipette cover these spots with water and let it remain for ten or fifteen minutes; then with the pipette remove the liquid and examine the products it holds in solution.  Afterwards make a comparative experiment on another part of the paper which is neither spotted nor whitened.

If the original writing has been done with a very acid ink on a paper containing a carbonate, such as calcium carbonate, the ink, in attacking the calcareous salt, stains the paper, so that if the forger has removed the ferruginous salts this removal is denoted by the semi-transparence that water gives to the paper.

To study carefully the action of the water it is necessary to repeat the experiment several times, allowing the paper to dry thoroughly before recommencing it.

According to Tarry, it is necessary to have recourse to alcohol to discover whether the paper has been scratched in any of the parts and then covered with a resinous matter to prevent the ink from blotting.

Place the document on a sheet of white paper and with a paint brush dipped in alcohol of specific gravity 0.86 or 0.87 cover the place supposed to have been tampered with.  It may be discovered if the writing thickens and runs when the alcohol has dissolved the resin.

Hold the paper moistened with alcohol between the eye and the light; the thinning of the paper shows the work of the forger.

Some more skillful forgers use paste and resin at the same time to mask their fraudulent operations; in this case luke-warm water should be first employed and then alcohol; water to dilute the paste, and alcohol to dissolve the resin.  The result is that the ink added on the places scratched out spreads, and the forgery is easily seen.

Test-papers (litmus, mauve, and Georgina paper) serve to determine whether a paper has been washed either by the help of chemical agents, acids incompletely removed, or the surplus of which has been saturated by an alkali, or by the help of alkaline substances.  The change of the color to red indicates an acid substance; an alkali would turn the reddened litmus paper to blue, and the mauve and Georgina test-papers to green.

Take a sheet of test-paper of the same dimensions as the document to be examined, moisten it, and cover it underneath with a sheet of Swedish filter-paper.  These two sheets together (the filter-paper underneath) are then applied to the document which has been moistened already.  The whole is then laid between two quires of paper, covered by a weighted board, and left in this condition for about an hour.  At the end of this time examine the test-paper to see if it has partly or altogether changed color.  This examination finished, put the test-paper in contact with distilled water, to be afterwards removed and tried by appropriate tests to discover the nature of the alkali or acid present.