Part 260

The consistency of a printing ink must be such that it passes on to the printing rollers at the proper rate. It will be obvious that various consistencies are demanded according to the nature of the machine used by the printer. For a rotary machine which prints many thousands of copies an hour a much thinner ink will be necessary than that required for art printing or for slow presses. As regards color, ordinary printing ink should be a pure black. For economy’s sake, however, newspaper printers often use an ink so diluted that it does not look deep black, but a grayish black, especially in large type.

The question of the time that the ink takes to dry on the paper is a very important one, especially with ink used for printing newspapers which are folded and piled at one operation. If then the ink does not dry very quickly, the whole impression smudges and “sets off” so much that it becomes illegible in places. Although it is essential to have a quick drying ink for this purpose, it is dangerous to go too far, for a too quickly drying ink would make the paper stick to the forms and tear it. A last condition which must be fulfilled by a good printing ink is that it must be easy of removal from the type, which has to be used again.

No one composition will answer every purpose and a number of different inks are required. Makers of printing inks are obliged, therefore, to work from definite recipes so as to be able to turn out exactly the same ink again and again. They make newspaper ink for rotary presses, book-printing inks, half-tone inks, art inks, etc. As the recipes have been attained only by long, laborious, and costly experiments, it is obvious that the makers are not disposed to communicate them, and the recipes that are offered and published must be looked upon with caution, as many of them are of little or no value. In the recipes given below for printing inks, the only intention is to give hints of the general composition, and the practical man will easily discover what, if any, alterations have to be made in the recipe for his special purpose.

Many different materials for this manufacture are given in recipes, so many, in fact, that it is impossible to discover what use they are in the ink. The following is a list of the articles commonly in use for the manufacture of printing ink:

Boiled linseed oil, boiled without driers.

Rosin oil from the dry distillation of rosin.

Rosin itself, especially American pine rosin. {409}

Soap, usually rosin-soap, but occasionally ordinary soap.

Lampblack and various other pigments.

By the most time-honored method, linseed oil was very slowly heated over an open fire until it ignited. It was allowed to burn for a time and then extinguished by putting a lid on the pot. In this way a liquid was obtained of a dark brown or black color with particles of carbon, and with a consistency varying with the period of heating, being thicker, the longer the heating was continued. If necessary, the liquid was then thinned with unboiled, or only very slightly boiled, linseed oil. Lampblack in the proper quantity was added and the mixture was finally rubbed up on a stone in small quantities at a time to make it uniform.

«Boiling the Linseed Oil.»—This process, although it goes by the name of boiling, is not so in the proper sense of the word, but a heating having for its object an initial oxidation of the oil, so that it will dry better. Linseed oil is a type of the drying oils, those which when exposed in thin coats to the air absorb large quantities of oxygen and are thereby converted into tough, solid sheets having properties very similar to those of soft India rubber. The process goes on much faster with the aid of heat than at the ordinary temperature, and the rate at which the boiled oil will dry in the ink can be exactly regulated by heating it for a longer or shorter time. Prolonged heating gives an oil which will dry very quickly on exposure in thin coats to the air, the shorter the heating the more slowly will the ink afterwards made with the oil dry.

Linseed oil must always be boiled in vessels where it has plenty of room, as the oil soon swells up and it begins to decompose so energetically at a particular temperature that there is considerable risk of its boiling over and catching fire. Various contrivances have been thought out for boiling large quantities of the oil with safety, such as pans with an outlet pipe in the side, through which the oil escapes when it rises too high instead of over the edge of the pan, and fires built on a trolley running on rails, so that they can at once be moved from under the pan if there is any probability of the latter boiling over. The best apparatus for preparing thickened linseed oil is undoubtedly one in which the oil offers a very large surface to the air, and on that account requires to be moderately heated only. The oil soon becomes very thick under these conditions and if necessary can be diluted to any required consistency with unboiled oil.

In boiling linseed oil down to the proper thickness by the old method there are two points demanding special attention. One is the liability of the oil to boil over, and the other consists in the development of large quantities of vapor, mostly of acroleine, which have a most powerful and disagreeable smell, and an intense action upon the eyes. The attendant must be protected from these fumes, and the boiling must therefore be done where there is a strong draught to take the fumes as fast as they are produced. There are various contrivances to cope with boiling over.

«Savage’s Printing Ink.»—Pure balsam of copaiba, 9 ounces; lampblack, 3 ounces; indigo and Prussian blue, each 5 drachms; Indian red, 3⁠/⁠4 ounce; yellow soap, 3 ounces. Mix, and grind to the utmost smoothness.

«Toning Black Inks.»—Printers’ inks consisting solely of purified lampblack and vehicle give, of course, impressions which are pure black. It is, however, well known that a black which has to a practiced eye a tinge of blue in it looks much better than a pure black. To make such an ink many makers mix the lampblack with a blue pigment, which is added in very fine powder before the first grinding. Prussian blue is the pigment usually chosen and gives very attractive results. Prussian blue is, however, not a remarkable stable substance, and is very apt to turn brown from the formation of ferric oxide. Hence an ink made with Prussian blue, although it may look very fine at first, often assumes a dull brown hue in the course of time. Excellent substitutes for Prussian blue are to be found in the Induline blues. These are very fast dyes, and inks tinted with them do not change color. As pure indigo is now made artificially and sold at a reasonable price, this extremely fast dye can also be used for tinting inks made with purified lampblack.

«To Give Dark Inks a Bronze or Changeable Hue.»—Dissolve 1 1⁠/⁠2 pounds gum shellac in 1 gallon 65 per cent alcohol or cologne spirits for 24 hours. Then add 14 ounces aniline red. Let it stand a few hours longer, when it will be ready for use. Add this to good blue, black, or other dark ink, as needed in quantities to suit, when if carefully done {410} they will be found to have a rich bronze or changeable hue.

«Quick Dryer for Inks Used on Bookbinders’ Cases.»—Beeswax, 1 ounce; gum arabic (dissolved in sufficient acetic acid to make a thin mucilage), 1⁠/⁠4 ounce; brown japan, 1⁠/⁠4 ounce. Incorporate with 1 pound of good cut ink.

«INKS FOR STAMP PADS.»

The ink used on vulcanized rubber stamps should be such that when applied to a suitable pad it remains sufficiently fluid to adhere to the stamp. At the same time the fluidity should cease by the time the stamp is pressed upon an absorbing surface such as paper. Formerly these inks were made by rubbing up pigments in fat to a paste. Such inks can hardly be prevented, however, from making impressions surrounded by a greasy mark caused by the fat spreading in the pores of the paper. Now, most stamping inks are made without grease and a properly prepared stamping ink contains nothing but glycerine and coal-tar dye. As nearly all these dyes dissolve in hot glycerine the process of manufacture is simple enough. The dye, fuchsine, methyl violet, water blue, emerald green, etc., is put into a thin porcelain dish over which concentrated glycerine is poured, and the whole is heated to nearly 212° F. with constant stirring. It is important to use no more glycerine than is necessary to keep the dye dissolved when the ink is cold. If the mass turns gritty on cooling it must be heated up with more glycerine till solution is perfect.

In dealing with coal-tar dyes insoluble in glycerine, or nearly so, dissolve them first in the least possible quantity of strong, hot alcohol. Then add the glycerine and heat till the spirit is evaporated.

To see whether the ink is properly made spread some of it on a strip of cloth and try it with a rubber stamp. On paper, the separate letters must be quite sharp and distinct. If they run at the edges there is too much glycerine in the ink and more dye must be added to it. If, on the contrary, the impression is indistinct and weak, the ink is too thick and must be diluted by carefully adding glycerine.

Aniline colors are usually employed as the tinting agents. The following is a typical formula, the product being a black ink:

I.—Nigrosin 3 parts Water 15 parts Alcohol 15 parts Glycerine 70 parts

Dissolve the nigrosin in the alcohol, add the glycerine previously mixed with the water, and rub well together.

Nigrosin is a term applied to several compounds of the same series which differ in solubility. In the place of these compounds it is probable that a mixture would answer to produce black as suggested by Hans Wilder for making writing ink. His formula for the mixture is:

II.—Methyl violet 3 parts Bengal green 5 parts Bismarck green 4 parts

A quantity of this mixture should be taken equivalent to the amount of nigrosin directed. These colors are freely soluble in water, and yield a deep greenish-black solution.

The aniline compound known as brilliant green answers in place of Bengal green. As to the permanency of color of this or any aniline ink, no guarantee is offered. There are comparatively few coloring substances that can be considered permanent even in a qualified sense. Among these, charcoal takes a foremost place. Lampblack remains indefinitely unaltered. This, ground very finely with glycerine, would yield an ink which would perhaps prove serviceable in stamping; but it would be liable to rub off to a greater extent than soluble colors which penetrate the paper more or less. Perhaps castor oil would prove a better vehicle for insoluble coloring matters. Almost any aniline color may be substituted for nigrosin in the foregoing formula, and blue, green, red, purple, and other inks obtained. Insoluble pigments might also be made to answer as suggested for lampblack.