WRITING INK Ink.—Inks are of several classes, as writing inks, marking or indelible inks, and printing inks. Writing inks may be black or colored. Black writ ing inks are chiefly nutgall iron inks, made from a solution of Aleppo nut galls with copperas; chrome logwood inks, made by the addition of 1 part of potassium chromate to 1,000 parts of saturated solution of logwood; aniline inks, made of coal-tar products, as nigrosine, eosin, etc., and carbon inks, made of a resinous alkaline solution mixed with lampblack. Marking inks are chiefly lampblack, or nitrate of silver. Colored inks are now made chiefly of aniline coal-tar products. It is important to understand the na ture of these different materials in order to choose the various kinds of ink required; to make them properly, if desirable, either for home use or for sale; to keep them properly, and to erase them when they produce any accidental stains. These points are the more important for the reason that since the use of coal-tar colors or aniline dyes, especially nigrosine, dating from about 1867, old-fashioned recipes for taking out ink stains have become untrustworthy. Unfortunate ly, a great many of these recipes taken from old books are still being published. Hence care must be taken not to be misled by instruc tions which were correct when they were first given, but can no longer be relied on.
To Make Black Ink. — Formerly black ink was usually made by ex posing to the air a solution of green vitriol in an infusion of gallnuts in water containing dissolved gum, sug ar, or mucilage. The result was a fine precipitate of tannate of iron held in suspension by the gum. Writ ing done with these inks was of a pale brown color, which, however, turned black on the paper. They are still in use, and recipes for making them will be given; but they are open to the objections that they corrode steel pens, tend to settle on standing, and the writing fades to a yellow or brown tint with age. Many old letters dat ing from war times are in existence the writing of which is almost faded from the paper.
Modern inks of this sort are im proved by the addition of a little free sulphuric acid, which prevents the tannate of iron from forming a precipitate or powder. Hence they are true solutions. The addition of a little indigo, carmine, or aniline blue is also an improvement. This is one of the reasons why modern inks can not be removed by old-fashioned rec ipes, the acids which take out the stain of tannate of iron having no ef fect on the modern coal-tar colors.
Inks of this class are made com mercially from Aleppo nutgalls and copperas, or from green vitriol. The nutgalls contain 60 to 70 per cent tannic acid and 3 to 5 per cent gallic acid. The galls are crushed, steeped in hot, not boiling, water, and strained.
The infusion is mixed with a solution of copperas containing free sulphuric acid. Indigo and aniline blues are added, and also a solution of gum arabic, the last ingredient enabling the writer to make light strokes with the pen and to prevent the ink from spreading too quickly. An antiseptic, usually carbolic or salicylic acid, is added to prevent mold.
Some experiments will be required to make a good ink of this class, as the amount of tannin contained in nutgalls varies, and the amount ex tracted by inexperienced persons va ries still more. Recipes will be given for the use of nutgalls, but for home made inks it will be found more con venient, when possible, to buy tannic and gallic acids ready made than to extract them from nutgalls. We rec ommend for a good homemade ink the following: Five ounces of tannin, 4 ounces of copperas, ounce of indigo, carmine, or aniline blue, and 10 drops of sul phuric acid.
Or 5 ounces of gallic acid, 74 ounces of copperas, ounce of indigo, car mine, or aniline blue, and 12 drops of sulphuric acid. The latter formula gives a finer quality of ink than the former, but it does not turn black so quickly. Hence a still better formula is a mixture of the two.