Scientific American 20, 13.11.1869
No doubt all of our readers are acquainted with the mica which is so extensively used in doors of stoves. But it may be stated that under this term a whole group of minerals is comprised, either occurring massive or disseminated in rocks. They have all a more or less foliated structure and pearly luster. They are elastic, transparent, or translucent, and have a specific weight of 2.7. In Germany mica has recently found application for the production of broom-like colors which bear the names "brocades," "crystal colors," and "mica bronzes." The mineral is to this end well crushed, boiled in hydrochloric acid, then washed with water, and assorted according to the size of the laminæ. Mica scales thus obtained exhibit a glass-like luster combined with a silver-white appearance.
The advantages of these brocades (which by the way may be colored) over the ordinary metallic brocades, are stated to be the following:
1. They do not cuntain any ingredient injurious to health.
2. They possess metallic luster like the ordinary brocades, and some surpass them even in liveliness of color.
3. Brown, black, blue, green, and rose, are obtained in remarkable beauty, which is not the case with the metal bronzes.
4. They comport themselves with perfect neutrality toward sulphurous exhalations.
5. Their specific weight being very slight, their yield is consequently correspondingly great.
In their application they may be fixed upon all kinds of articles of metal, wood, glass, plaster-of Paris, and paper board. They are consequently well adapted to the preparation of artificial flowers, fancy papers, sealing-wax, in tapestry, furniture-making, and painting. Theaters may employ them for imitating gold-rain and snow, for which purpose they recommend themselves on account of their lightness and cheap price. In short, they may be used for almost all the purposes to which the ordinary bronze powders have been applied. In fixing these brocades upon articles of any kind it is advisable to paint them first with a color aimilar to that of the bronze; for silver, a ground of white lead is suitable; for blue, one of ultramarine, etc. They are equally suitable for oil and glue colors, which latter are fixed with a mixture of four parts of glue and one of glycerin. Upon this rust, when hard, the binding material for the brocade is spread, and after one quarter of an hour this latter is sifted over.
As binding material a paste, consisting of four parts of boiled starch and one of glycerin, is recommended. If desirable, the powder may be finally pressed down with a roller. If the ground is formed by an oil paint, the binding material for the brocade should be constituted of a dammar, or pale copal varnish, upon which, when only pitchy, the powder is sifted over. When finally coated with a suitable spirit, dammsr, or copal varnish, the so-prepared articles ammo a luster which, in beauty and durability, far surpasses any heretofore ob-tained with the common bronzes. When small particles of mica-silver are spread over articles coated with asphalt varnish, the result is a good incitation of granite. The crystal colors are also suitable for calico printing, and fabrics upon which they are applied, surpass in brilliancy tbe heavy bronze and glass-dust fancy fabrics from Lyons. Employed between or on colored gelatin plates, they give, rise to superb crystallizations, whisk are used as inlayings for buttons and various other articles. They may be spread over finished porcelain and glassware, if these are heated again to the fusing point of their glazing.
According to Hr. C. Cock and L. Schneider, in Prague, these brocades may be colored with the following dye stuffs: Rose, with a decoction of cochineal; carmoisin, with the bluish magenta red; bright red, with fuchsine and Havana brown; violet, with Hofman's violet. A solution of Prussian blue in oxalic acid, serves for producing a bright blue, and Girard's violet for deep blue; light and dark green art imparted by aniline green and curcuma; gold with curcuma, dark brown with a proper bark extract, and black with litmus and haematoxylin or logwood extract. Silver needs no color.
According to Dr. L. Feutchwanger's (vide his popular "Treatise on Gems"), mica is found in this country at Williamsburg, Mass., Hartford, Conn., and many other places. The green mica, which is of a beautiful grass-green color, is found in Brunswick, Me. The rose-red mica, which is also a very beautiful mineral, in principally found at Goshen, Chesterfield, Mass., Acworth, N. H., Bellows' Falls, Vt., etc. Mica, according to the above-named mineralogist, when of good colors, may be used for jewelry and other ornaments.
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