7/27/2023 0 Comments Cobalt blue and ultramarine blueThese blues are for many purposes more desirable than some of the artificial ultramarine blues, as they make colder blue tints with white, not leaning so much to the purple or violet rays. When pale shades are required, a portion of French process zinc oxide added to the blue will produce very fine light effects. 9, another lower-priced brand being marked C. Imitation of cobalt blue is offered to the color grinding trade in various depths of shade, the marks of the best quality being C. The latter show a far more brilliant color effect, much stronger hiding and staining power and are not affected so much in tone by electric or gaslight. Its cost being prohibitive, it is not placed on the market as a coach color or as an enamel.Ĭobalt blue smalts, a glass consisting of a double silicate of cobalt and potash with such impurities as the oxides of iron and calcium, was very largely ground up in various vehicles and sold as cobalt blue before the advent on the market of the lower-priced imitation of cobalt blue made by the manufacturers of artificial ultramarines. It has also been known as Thenard's blue and azure blue. True cobalt blue is readily distinguishable from its imitation by being unaffected in contact with acids and strong alkalies that affect the artificial brands. Cobalt blue has a greenish tone, that when viewed under gaslight is more or less violet. Grinding it for artists' use in oil to be put up in tubes will require 35 per cent dry pigment to 65 per cent by weight of bleached poppyseed or nut oil, either of which is preferable to linseed oil for this purpose. It works better as a water color than it does in oil, and is highly valued on that account among moist colors used by artists. True or genuine cobalt blue is a compound of the oxides of cobalt and alumina with some phosphoric acid, occasionally. However, the latter should not be put up for the use of the artist, excepting when label states plainly that it is artificial or imitation. While true cobalt blue is of great permanency and unaffected by the most destructive agencies, it is too high in cost for general use, and really the artificial ultramarine, sold as imitation of cobalt blue, gives a much more brilliant color effect. True cobalt blue is only interesting to the color grinder so far as its use by artists is concerned, while for all other purposes the artificial ultramarine, known to the trade as imitation of cobalt blue, which can be obtained in several grades and shades, is being placed at the disposition of the consumer.
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