While government service specifications, when sending proposals for chrome green to manufacturers, call for an intimate mixture of at least 98 per cent chrome yellow and Prussian blue, permitting the presence of not over 10 per cent lead sulphate, the color consuming trade in general has very little use for a green of that composition for many reasons, although on some occasions chemically pure chrome green is called for, as will be seen below. In these instances, however, there is no restriction as to the percentage of lead sulphate present and the color grinder, when purchasing dry chrome green of chemical purity, will select those of the greatest staining power at equal price. If lead sulphate is present in excess, this will show up in the testing of tinctorial strength. As a matter of course, he will also consider richness of tone, softness of texture and oil absorption, as no matter how high the price of oil may go, it will hardly ever reach the price of chemically pure chrome green, pound for pound.
Some twenty or thirty years ago the trade did not think of purchasing any so-called chrome green that did not carry in its pigment portion anywhere from 80 to 90 per cent by weight of barytes, and some proprietary brands of this green that carried in the pigment as much as 25 per cent coloring matter found a ready market at fair prices. The chemically pure green being so very opaque and of such great tinctoral power, it was deemed unwise and wasting money not to extend the pigment with barytes to the extent mentioned. Later on, when the crusade for pure colors was under way, the paint and color grinders, by common consent, adopted 25 per cent color and 75 per cent barytes as a standard for a medium shade of chrome green, with a slight variation for the deeper shades. In those days the Bureau of Engraving and Printing at Washington bought their annual supply of chrome green for plate ink of that composition. To-day this branch of the government service purchases chrome yellow of the pale lemon shade and Prussian blue, doing the mixing themselves and adding base white or barytes, according to a formula that is a department secret. The most prominent manufacturers of wire cloth at that time purchased the green for painting the cloth ground in oil, using many tons during each season of a blue toned chrome green of the 25 per cent pure color and 75 per cent barytes type. They found, however, much loss by settling in the dipping tanks and changed to 50 per cent pure color and 50 per cent clay in the pigment and still later found that the chemically pure green was cheapest for their use in the end. About five or six years since the wire cloth makers agreed to abandon the use of green on wire cloth and to print the cloth in black only. That green wire cloth was less in demand may be accounted for by the fact that some manufacturers used greens for painting the cloth that were not even ground in paste form, but dry green job lots, simply mixed with inferior thinners. The consequence as a rule was, that the cloth, when in the storerooms of jobbers and dealers but a short time, lost its coating of green paint by flaking off at the slightest touch. Numerous have been the attempts of color makers to furnish chrome greens to grinders on other bases than barytes, but all of them have proven futile, so far as their use for the painter was concerned, because painters, especially house painters, want a green that has a tooth and filling properties, both of which are furnished by fine barytes. So long as chrome green in oil, when properly thinned for exterior work, as trimmings, blinds, etc., covers fairly well in one coat over a lead colored primer, it is the material desired by that class of trade.
The Grinding of Chrome Green in Oil for the trade is still done by many color grinders in the same manner as it was in the long ago, that is, they purchase various shades of chrome green that are extended by the color maker with barytes, either in the precipitation tank or on a mill by mixing barytes with dry chrome green that has probably been stretched or extended in the wet way, the additional barytes being added simply to meet lower prices. Trial mixings and grindings made years ago by several firms to produce commercial or proprietary brands of chrome green in oil by mixing certain portions of chemically pure green, barytes and oil, instead of mixing and grinding the dry extended green in oil, failed, as it was found, on long standing, that the grinding was not homogeneous, the color on opening containers set aside for six months or more, floating on top, while the barytes had caked in hard sediment in the bottom and was found almost devoid of color. Whether this was due to the coarse nature of the barytes or to the use of a poorly made chemically pure green, was difficult to determine. We believe both factors helped to make the scheme a failure. Yet there was one color manufacturer in the country who conceived and carried out this idea, not only in greens, but in other strong colors, and who thus simplified his manufacturing methods and grew immensely rich thereby. Instead of having a dozen or more lots of greens of various compositions, he got along with a stock of three or at most four shades of chemically pure chrome greens, which he had ground fine in oil, then added as his trade required it, a certain percentage of fine floated barytes and sufficient additional oil, giving this mixture one final run through the mill, thus obtaining a smooth paste that was liked by the trade and for which he obtained better prices than most color grinders who spent more money for manipulating a lot of barytes green through the mills. His wisdom was in keeping a very large stock of one grade of barytes only and that of the whitest and finest floated grade, while other color grinders and color makers proved penny wise and pound foolish by purchasing off colored and coarse barytes, thinking that anything was good enough in a color like green in their desire to save a few dollars per ton. Furthermore, the color grinder referred to, by following his method was always assured of uniformity of the goods, a feature that is doubtful when the extended dry green is purchased or made in the same factory where it is afterwards ground in oil. The failure above referred to strengthened the belief on the part of some color grinders and color makers that in order to make an extended green that would not separate after being ground in oil, it was necessary to make it in the color maker's tub, so as to color or rather fasten the color on the barytes, which is or at least appears to be an unconfirmed theory, as a mixture of Prussian blue and chrome yellow cannot act as a dye upon a substance like barytes. It is simply a mechanical mixture in either case, no matter how it is done.