The colored writing inks, of which "red" is the more important, are in great number and with hardly an exception at the present time, manufactured by adding water and water-glass to a soluble aniline red color. Cochineal which was used for red ink formerly is now almost obsolete. Nigrosine, one of the best known of them, is much used as a cheap "black" ink, but as it is blue black and never becomes black, it really belongs to the family of "colored" writing inks. They possess an undeserved popularity for they flow freely from the pen which they do not corrode, nor do they thicken or spoil in the inkwell; they are however very "fugitive" in character and should not be employed for record, legal, monetary or other documentary purposes. The indigo and prussian blue inks are well known, the former under certain conditions a very permanent ink, the latter soon disintegrating.
Copying inks are of two kinds, one dependent on the addition of glycerine, sugar, glucose or like compounds to the black writing inks or chemical writing fluids heretofore mentioned, which are thereby kept in a moist offsetting condition; the other due to the solubility of the pigmentary color with water, such as the aniline inks which are given more body than those for ordinary purposes--and the logwoods in which the pigment is developed and given copying qualities by chemicals, and hence becomes responsive to the application of a sheet of paper dampened with water. Copying ink should never be used for "record" purposes as it is affected by changes of the temperature.
India ink, sometimes called China ink, or as formerly known by the ancients and in classical and later times "Indian ink," is now used more for drawing and engrossing than it is for commercial purposes. It belongs to the "carbon" class and in some form was the first one used in the very earliest times. In China it is applied with a brush or pith of some reed to the "rice" paper also there manufactured. It is easily washed away unless bichromate of ammonium or potassium in minute quantities be added to it, and then if the paper on which it appears be exposed for a short time to the action of the actinic rays of sunlight, this gummy compound will be rendered insoluble and cannot be removed with any fluid, chemical or otherwise.
It possesses also great advantages in drawing, since it acts as a paint, and will give any degree of blackness according to the quantity of water mixed with it.
Secret or sympathetic inks are invisible until the writing is subjected to a subsequent operation, such as warming or exposing to sunlight. To further aid the object in view, the paper may be first steeped in a liquid and the writing only made visible by using another liquid which has some chemical affinity with the previous one. The number of this kind were but few but have multiplied as chemistry progressed.
The ancients were acquainted with several modes.
Ovid indiscreetly advises the Roman wives and maidens if they intend to make their correspondence unreadable to the wrong persons to write with new milk, which when dried may be rendered visible by rubbing ashes upon it or a hot iron. Pliny suggests milky juices of certain plants of which there are a considerable variety.
Indelible ink is not used for writing purposes on paper, but is found best adapted for marking linen and cancellation or endorsing purposes. It is chiefly composed of nitrate of silver preparations, to which heat must be applied after it has been dried; or a pigment is commingled with the same vehicles used in making common printing ink and in its use treated as such.
Diamonds, gold, silver, platinum and a host of other materials are manufactured into ink and are to be placed under the head of miscellaneous inks. They are in great number and of no interest in respect to ink writing except for engrossing or illuminating.
Still another ink once held in much esteem and now almost obsolete is the so-called "safety" ink.
Manufacturers, chemists and laymen in great number for many years wasted money, time and energy in diligent worship at a secret shrine which could not give the information they sought. A summary of the meager and barren results they secured is of little value and unimportant. Hence, there is no REAL "safety" ink.
It is true that lampblack (carbon) as made into ink, resists any chemical or chemicals, but simple water applied on a soft sponge will soon remove such ink marks. The reason for this is obvious, the ink does not penetrate the paper.
"Safety" ink which will not respond to acids may be affected by alkalis, or if resisting them separately, will yield to them in combination.
