Antwerp blue is now seldom in demand, although up to about fifteen years ago it was called for ground in poppyseed oil for artists' use, also in japan and varnish for special coach work, and even in water for fresco work. At that time it was imported from France or Belgium packed in cases of ten kilos and marked "Bleu Mineral" (mineral blue). It is as difficult to obtain it to-day from New York importers as it is to find a needle in a haystack. There is nothing so remarkable about the color or tone of this blue, but, while the text books say that it is almost identical with Prussian blue, only paler in color, the color grinder will find it extremely difficult to match the particular shade of the Antwerp blue that is furnished in artists' tubes by Winsor and Newton and Continental manufacturers of artists' colors. Some color maker friend will tell him to take three or four pounds Prussian blue and one pound alumina hydrate, mixing the two pigments and have the exact tone and shade, but if he accepts the advice he will be disappointed. Our advice is to select a Prussian blue that lacks the bronze cast, but is strictly pure, adding one part finest blanc fixe by weight to two parts of the dry blue, and if the shade is not pale enough lighten the color with the addition of as little French zinc white as possible. Made by this method, the pigment is not so apt to liver in oil or japan as it is when made with alumina hydrate, besides it will have better body. To grind in poppyseed oil, figure on 35 per cent vehicle and 65 per cent pigment, for coach color figure on 40 per cent gold-size japan and 60 per cent pigment, for distemper color figure on equal parts pigment and water for mixing.
Berlin blue is not listed in the catalogues of paint manufacturers in the United States. The pigment belongs to the Prussian blue group and the name simply a synonym for commercial purposes. Will be dealt with under "Prussian Blues."
Bremen blue consists mainly of hydroxide of copper CuH202) with small portions of copper carbonate (CuC03), and so far as its use in oil is concerned it is obsolete. Even in its dry form, as it was sold to decorators for distemper and fresco painting, it has been replaced by ultramarine blue and imitation of cobalt blue.
Blue verditer, a copper blue very similar to Bremen blue, is still in use by artists to a small extent, both in oil and in water, especially in the latter form, but, not being permanent to light, the demand is very limited. The pigment varies considerably, according to the method of manufacture, hence it is difficult to give an accurate figure as to its absorption of oil in grinding, but 40 per cent poppyseed or nut oil and 60 per cent by weight of pigment is about a good average to figure on.
Brunswick blue is simply an extended color, consisting of Prussian blue and barytes and in such proportions as the fancy of the maker or his selling price and profit-making idea would dictate. It may consist of 10 per cent Prussian blue and 90 per cent barytes or of equal parts blue and barytes, and it is not at all necessary to have the blue extended by the color maker - in fact, it is far more economical and more accurate to let the addition of the extender be made in the mixer when getting ready to grind it in oil. To make a batch of 100 pounds of Brunswick blue in oil with only 10 per cent color in the dry pigment, place in the mixer seventeen pounds Prussian blue that has been ground fine in linseed oil in the proportions of equal parts by weight of pigment and oil, add seven pounds more raw linseed oil and seventy-six pounds finest floated barytes. If the blue is free of paint skins and the barytes really fine, a thorough mixing will make the paste smooth enough for such a low-priced blue, otherwise run it through a mill until smooth and fine.
Taking for granted that the Brunswick blue is to consist of 50 per cent pure color in the dry pigment, a mixing on these figures will give the desired result: - Sixty-five pounds Prussian blue in oil, as above, add thirty-two and one-half pounds of finest barytes and two and one-half pounds raw linseed oil, and follow above suggestions.
This suggestion would apply also to this blue in japan, with this proviso, however, that here a 10 per cent pure color in the pigment would not answer, but, figuring on a blue to consist of 50 per cent pure coloring matter and 50 per cent barytes, we would conclude that the mixing should be based on the following: - Place in the mixer seventy pounds pure Prussian blue that has been ground fine at the rate of 40 per cent pigment to 60 per cent by weight of gold-size japan and add twenty-eight pounds finest floated barytes (bone dry) and two pounds gold-size japan or good rubbing varnish. Mix thoroughly and if not smooth enough give it one run through mill to finish. This is not pure Prussian blue, and it is not to be offered as such, but as Brunswick blue in japan, and if the materials are all right in the first place it will be an excellent working material. It is made on the same plan and rather a little better than the coach colors and colors in oil that made one manufacturer immensely rich some thirty-five years ago.