In this line we find the chrome greens, when so listed of the same type, as the 25 per cent greens in oil, while those listed as coach painters' green are usually stronger in color, running as high as 33 to 40 per cent actual color and in some rare instances as high as 50 per cent. Some proprietary brands, such as brilliant green, and a few others with fancy names, such as full strength green, are chemically pure, while milori green is of varying composition, anywhere from 50 per cent color to pure. This latter green should be a peculiarly rich shade of green to deserve that name, but such is not always the case. Chrome green for coach and car work is best ground in gold size japan, because the brown color of ordinary color grinding japan is apt to have an effect on the tone of the green in drying out on the surface and the subsequent coats of varnish cannot overcome this, nor can a coat of color and varnish remedy such defect. When figuring on the proportions of pigment and japan necessary for grinding these greens in japan, it is necessary to allow for the loss by evaporation of the volatile portion of the japan, which sometimes is quite large. Assuming that a deep shade of chemically pure chrome green, which, if ground in oil, requires thirty-two pounds liquid to sixty-eight pounds of dry color, it will require forty pounds gold size japan to from sixty-three to sixty-four pounds color to produce one hundred pounds of the finished product, which must be ground on a water cooled esopus stone mill of not over twenty-inch. diameter, with a speed of not over thirty-six to forty revolutions per minute, as the temperature of the color should never exceed 110° F. Chrome greens are very delicate and easily spoiled by overheating. If water cooled stone mills are not part of the apparatus at the disposal of the color grinder, a water cooled iron mill of sixteen or eighteen-inch diameter will do the work, provided the grinding surface is not too dull.
This applies equally to the extended chrome greens in japan, a 25 per cent green requiring, if of medium shade, eighty pounds pigment and twenty-three pounds of gold size japan to produce one hundred pounds finished color. Here the color grinder will find it of advantage to make two operations, which may seem a trifle out of the way, but will make a better product at less cost for power and wear on the mills. Instead of mixing the dry color and barytes in the gold size and giving the mixture several runs, the chemically pure green is first ground fine or almost fine in the japan and the barytes added to the product on the last run with the additional thinners, if any be required. For the 25 per cent green of medium shade as above, grind twenty pounds chemically pure green, in say twelve pounds gold size japan, and add to this on last run sixty pounds barytes and ten pounds more of gold size japan. This should produce 100 pounds of quick drying, medium chrome green, that when thinned with pure spirits of turpentine, will cover very well on coach or fine wagon gears or bodies over the proper ground work, even in one coat. Many so-called express greens are of this type when a green of blueish tone is used.
When a very deep shade of chrome green in japan is wanted in this commercial quality, less pigment and more gold size japan is required, same as is the case in an oil color green. For instance the shade is extra dark, grind nineteen pounds of the chemically pure green of that shade in say fourteen pounds of gold size japan to standard fineness, add fifty-seven pounds dry barytes and twelve pounds more of gold size japan, run the mixture through the mill once or twice more and the product should be 100 pounds quick drying, extra deep chrome green. It is self-evident that when this method of mixing and grinding is adopted the barytes must be of impalpable fineness and soft texture, and as blanc fixe (precipitated) barytes is not usually in fine powder, even when fairly soft in texture blanc fixe must be mixed with the dry green at the very start and both ground together in gold size japan to a finish. Taking for granted that a color grinder desires to place upon the market an extended chrome green of rather light specific gravity that will spread over more surface than the ordinary commercial brand of coach painters' green, and yet be lower in cost than a chemically pure chrome green, it is open to him to use blanc fixe in place of the natural floated barytes. Blanc fixe can be bought in the dry powder, but it is well to determine carefully that it is really dry, and the same is also necessary with the green before mixing with gold size japan, as the latter will not work well with moist or damp pigments of any kind. As first class blanc fixe absorbs nearly as much japan as would a light shade of chemically pure chrome green, the extra expense of its use is but little more than the difference in cost between it and the chemically pure green from the color grinder's standpoint. However, to the consumer who uses the green not for tinting, but for covering surfaces solidly, the price and the working properties of a green extended with blanc fixe in comparison with the chemically pure green has its meaning. Take as an example, a green composed in its pigment portion of 40 per cent by weight of color and 60 per cent by weight of blanc fixe, and figuring on an extra deep shade, the difference in the cost of the dry pigment alone is in favor of the extended green to the extent of from nine to ten cents per pound at present market rates. A green in japan of this composition will require twenty-six pounds chemically pure green, extra deep dry, thirty-nine pounds blanc fixe dry and thirty-eight pounds gold size japan for 100 pounds finished paste, and the bulk of the color will be very nearly as great as that of chemically pure green in japan. The lighter the shade the less japan will be required for mixing and grinding and the bulk of the color correspondingly less.
While chrome green extended with blanc fixe is not so apt to settle out when thinned for dipping as is often the case for small metal ware that is baked, it is always best to grind chemically pure green in varnish specially adopted for baking, so that when the base so ground is thinned with more varnish to the consistency for dipping, there will be no sediment, which would be apt to give trouble. For work of this kind chemically pure greens are none too strong, as the less color that is used, the better the working properties.
While chrome greens are to be found in the lists of tube colors, they are not used by artists of renown for picture painting, but are made use of by amateurs and professional sign writers, the latter using the large size tubes for the sake of convenience. It would be wasteful to mix and grind such greens in expensive poppyseed oil, as bleached or refined linseed oil will serve the purpose very well. The only difference that may be required is to grind the greens of whatever composition may be selected for the list to the utmost degree of fineness. Another point is, that chrome greens to be put up in tubes, should be held stouter than the commercial chrome greens that are put up in tin cans, so that when the color is squeezed out of collapsible tubes, the pigment is not so likely to separate from the oil. It does not as a rule require as much refined oil for the grinding of chrome green as it does of raw linseed oil, because refined linseed oil is more limpid. This is due to the removal in the refining process of mucilaginous matter and impurities, commonly known as linseed oil foots, which is always more or less present in raw linseed oil. Chrome green in water is very seldom, if ever, called for and may as well be omitted from distemper color lists, because when mixed with kalsomine for wall painting, it is not only apt to fade badly on account of the usual alkalinity of the white, but tints so made appear yellow under the effect of gas light or electric light.