Method of restoring decayed WRITINGS. In the 77th vol. of the Phil. Trans. there is a paper on this subject by Sir Charles Blagden. One of the best methods he found upon experiment to be, covering the letters with phlogisticated or prussic alkali, with the addition of a diluted mineral acid; upon the application of which, the letters changed very speedily to a deep blue colour, of great beauty and intensity. To prevent the spreading of the colour, which, by blotting the parchment, detracts greatly from the legibility, the alkali should be put on first, and the diluted acid added upon it.
Writings || Wurtemberg. The method found to answer best has been, to spread the alkali thin with a feather over the traces of the letters, and then to touch it gently, as nearly upon or over the letters as can be done with the diluted acid, by means of a feather or a bit of flick cut to a blunt point. Though the alkali should occasion no sensible change of colour, yet the moment the acid comes upon it, every trace of a letter turns at once to a fine blue, which soon acquires its full intensity, and is beyond comparison stronger than the colour of the original trace had been. If, then, the corner of a bit of blotting paper be carefully and dexterously applied near the letters, so as to imbibit the superfluous liquor, the staining of the parchment may be in a great measure avoided; for it is this superfluous liquor which, absorbing part of the colouring matter from the letters, becomes a dye to whatever it touches. Care must be taken not to bring the blotting paper in contact with the letters, because the colouring matter is soft whilst wet, and may easily be rubbed off. The acid chiefly employed was the marine; but both the vitriolic and nitrous succeed very well. They should be so far diluted as not to be in danger of corroding the parchment, after which the degree of strength does not seem to be a matter of much nicety.
Method of Copying Writings. The ingenious Mr Watt, about 16 years ago, invented a method of copying writings very speedily, and without the possibility of committing mistakes. A piece of thin unfixed paper is to be taken exactly of the size of the paper to be copied; it is to be moistened with water, or, what is better, with the following liquid: Take of distilled vinegar two pounds weight, dissolve it in one ounce of boracic acid; then take four ounces of oyster-shells calcined to whiteness, and carefully freed from their brown crust; put them into the vinegar, shake the mixture frequently for 24 hours, then let it stand until it deposits its sediment; filter the clear part through unfixed paper into a glass vessel; then add two ounces of the best blue Aleppo galls bruised, and place the liquor in a warm place, shaking it frequently for 24 hours; then filter the liquor again through unfixed paper, and add to it after filtration one quart, ale measure, of pure water. It must then stand 24 hours, and be filtered again if it flows a disposition to deposit any sediment, which it generally does. When the paper has been wet with this liquid, put it between two thick unfixed papers to absorb the superfluous moisture; then lay it over the writing to be copied, and put a piece of clean writing paper above it. Put the whole on the board of a rolling-press, and press them thro' the rolls, as is done in printing copperplates, and a copy of the writing shall appear on both sides of the thin moistened paper; on one side in a reversed order and direction, but on the other side in the natural order and direction of the lines.