Printing Inks, their Manufacture and Use

The following is a description of  printing inks and ink manufacturing in the early years of the 20th century. It is taken from an article by H.Y. Richardson of the Richardson Printing Ink Company Ltd, that appeared in the April 1908 edition of the British Printer.

The basis of all printing inks is colour (in which term is included black) and varnish, the latter serving as the vehicle or carrier of the former. Lamp-black is made by burning creosote or other oil in a chamber to which a quantity of air is admitted, insufficient for complete combustion. The result is the production of soot, just as an oil lamp produces smoke or soot when the supply of oil is too great, or the supply of air is too small. This soot or lamp-black is deposited in large chambers, from which it is collected. This class of lamp-black is used for news and the commoner kinds of inks. For the better sort, a black which is a product of the natural gas of America and elsewhere is preferred on account of its greater density of colour.

Dry Colours

The exquisite and brilliant colours known as anilines, ranging over the entire prismatic spectrum, crimsons, reds, oranges, yellows, greens, blues and violets, and including other colours such as browns and purples, are to a certain extent denied to the inkmaker, because many of them are fugitive, and therefore unworthy of use in "the art preservative of art." The ink maker uses, for his finest inks, only such coal-tar colours as are permanent, and he therefore relies for some of his best results on colours which are not of this series. He betakes himself to what we may describe as mineral colours, which include vermilion, the chromes, bronze, prussian and ultramarine blues, or the siennas and umbers, the two last belonging to, the group known as earth colours, owing to the fact that they are obtained as earths and are not manufactured. All dry colours are produced in the form of lumps or powders, which require to be broken down or ground down before incorporation with the varnishes. 

Varnishes

Many different varnishes are used by ink makers, but the principal ones are those prepared from resin and linseed oils respectively. The former is used for news and the commoner kinds of inks, the latter for the better sorts. 

The best oil is genuine, well matured, unadulterated, Russian Baltic linseed oil, costing a high price, and the worst are the rough, ill-matured Calcutta brands, which cost very much less, and which may be adulterated to any extent. An ill-matured oil is easily discovered when it is put into a varnish pot and heated, for it froths up and there are deposited what are technically known as " foots." The function of all varnishes is two-fold: 1.  To act as a vehicle or carrier of the colour. 2.  To act as a drying agent.  Without the vehicle it would be impossible to get the colour conveyed to the formes and blocks, and without this drying agent, the printed matter would never be got into the customers' hands in the marvellously short time in which this is effected. Linseed oil, when subjected to prolonged boiling at a high temperature, is converted into a varnish which has an extraordinary affinity for oxygen.

Ink Prepared from Linseed Varnish

Varnish greedily, absorbs oxygen from the air, and this converts it from a gummy substance into a compound which is solid at the ordinary temperature of the air, the ink, in fact, is dry! This drying operation is also assisted by the absorbent action of the printing paper and by other means known to certain ink makers. Thick varnish, having absorbed more oxygen during the boiling process, makes an ink having less drying power than one made from thin varnish, but a thick varnish carries more colour. 
Varnishes for special purposes, such as the manufacture of bronze blue ink, are "flared," which process consists in first heating the varnish and then setting it on fire, thereby removing all greasy matter. 
The colour is ground into the varnish in various proportions and for various lengths of time, but always so that the finest subdivision of the colour is obtained. With skilled workmen and ordinary care it is next to impossible to make a badly ground ink with the latest ink mills. 

Lithographic Inks

Lithographic inks are much stiffer than letterpress, and are made from specially prepared varnishes; they require more power to grind and contain more colour, and therefore usually cost rather more. A lithographic ink cannot be too well ground for the average high quality of work which is done with it on the delicate surface of the stone. It is very important that lithographic inks should be unaffected by the water used in this process, and also that they should be non-acid, otherwise the work on the stone becomes " eaten off." This last-named result is sometimes caused, however, by badly ground inks. 

The Mixing of Inks by the Printer

Unless the chemical composition of the dry colours used is known more or less, it is very hard to say what inks will mix, and the ink maker should be consulted. If a printer uses inks from one maker only, it is an easy matter for that firm to tell him which inks would, and which would not mix, since they would know what colours had been used in the inks. But it would be necessary for anyone else to make an analysis of the inks before being able to say definitely whether or not they would be affected by each other. Supposing a printer was to mix cadmium yellow with, say, flake white, he might be surprised to find the resulting colour blacken. This, however, is what might be expected when one remembers that cadmium yellow is the sulphide of cadmium and flake white is lead carbonate, and that the lead sulphide resulting from the mixture is black. Far and away the most common chemical action to be feared by careless mixing, is mixing a lead colour with one containing sulphur. 

Some inks do not work evenly, and this is specially noticeable in solid blocks, a mottled appearance being produced. The degree of mottle depends a great deal on the printer, some being able to get over the difficulty better than others. Bronze blues, ultramarine blues  and inks made from earth colours seem the chief offenders. The cause is to be found in the physical properties of the dry colours, some seeming to have less affinity for the varnish and not making so perfect a mechanical mixture

The earth colours, being particularly hard and difficult to grind, do not mix so readily with the varnish. The remedy, given that the printer has failed, is to let the ink maker know all the conditions under which the fault arose and to allow him to amend the ink to suit the particular work. Variation of covering power in given weights of ink occurs at times, and the cause lies again in the physical properties of the dry colour, which cannot always be explained. Nothing in the way of an alkali should be added to an ink, as many colours would be decomposed. Bronze blue, for instance, would be decomposed to iron oxide (rust). In the same way nothing having acid properties should be added, as an equally bad result might be produced. 

Whatever the ink, a thorough knowledge of the nature and speed of the printing machine, the kind of work to be done and the paper to be used is essential before the ink- maker can supply a satisfactory ink. It is an advantage if the ink seller possesses a thorough knowledge of papers and papermaking as he is then able to judge and even to advise as to what ink will best suit a given paper.