Scientific American 12, 11.12.1847
Every one may have noticed that paint in which white lead is mixed, after it has been applied a while, cracks, and scales off. This is explained by the fact that lead exerts a chemical action on oils, in consequence of which the oil, when in combination with the lead continues to harden, antil at last under the various changes of the atmosphere, it becomes brittle, breaks into scales, and cleaves off. On account of this action, it is thought that no white lead should be used in the "priming" coat, in painting buildings or articles which are not designed to be white. Black paint is more durable than white. This may have been noticed where, as on guideboards, &c., black letters have been formed on a white ground. The black remains perfect long after the surrounding parts have mouldered away, leaving the letters standing in "relief." This is explained as follows. The black paint is made chiefly of lamp black which substance is nearly pure carbon, and is known to be one of the most imperishable substances in nature—that it is not changed by the vegetable in combination with which it is used as paint. in consequence of which the slightest film cif the compound is a most durable protection against the destructive influences of the weather.
White lead will not scale off, unless varnish has been mixed with it, or the ground on which it is put, be either suffused with grease or rosin, as is often the case with pine wood.
A preventative for white lead paint turning yellow in dark situations would be a fortune to the discoverer.
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