The Manufacturer and Builder 5, 1873
615. Adulterated Ultramarine.
- How can I detect adulteration in ultramarine? I hear it is done often, and I think that the want of body which I find in some kinds is due to this. Is it done with heavy spar-like white lead? or with what? and how can I find out without going through the trouble of learning chemical analysis? - S. S., Painter, New York.
- Heavy spar is too ponderous to adulterate a paint less heavy than white lead. They use crystallized gypsum for this purpose, and you may easily detect it by placing some of the dry paint on paper and crushing or pressing it flat with a smooth hard surface; then take a common magnifying-glass and look at the mass, the gypsum particles constituting the adulteration will then be easily seen.
616. Making blue ultramarine.
- Is there a way to make blue ultramarine at once without at first making the green kind and changing it afterward into blue by a second calcination? - O. P., Subscriber, Brooklyn.
- Fustern recommends the following recipe for that purpose: sulphur, 120 parts; kaolin, 110; soda, 95; resin, 15; charcoal, 10; all well powdered, mixed in the mill, and heated in a round bellied pot for 15 to 20 hours.
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