Scientific American 25, 17.12.1859
There are several colors that are natural transparents; others that mat be made so by mixture.
The transparent colors are Terre de Sienna, Asphaltum, Dragon's Blood, Carmine, Rose Pink, Chemical Brown, all the Lakes, Gamboge, and all the Gums.
Semi-transparent - Umber, Vandyke Brown, Chrome Red, Emerald Green, Brunswick Green, Ultramarine, Indigo, Verdigris.
Remarks. - These colors should be ground very fine and spread on evenly.
If to be shown with a strong light two coats may be given; but if a subdued light one coat is better.
Transparent colors are purer if clutriated; that is, ground fine in water; let it settle; pour off the top part of the settling; mix that up with more water; let it settle, and take the top half of that, which will be free from all sand and grit. If the pure part of the pigment, however, should be the heaviest, discard the top and use the bottom of the sediment. Usually, however, the purest coloring part settles upon the top.
Any of these colors will work more evenly, and be more transparent, if a small quantity of water be mixed while grinding.
Turpentine makes transparent colors work crumbly.
Bleached boiled oil, or white varnish, is the best vehiche for flowing evenly. Raw oil does very well, only that transparent colors are always difficult to dry.
- The Painter's Manual.