Manufacturer and builder 11, 1871
Lead is the main constituent of many paints, as red-lead, white-lead of different kinds, Massicot, Cassel-yellow, and enters in all the chrome yellow, chrome-orange, and chrome reds, of which we have treated in our first volume. Generally lead, if used in metallic form in order to manufacture paints, should be pure, especially for making white-lead, as the clearest white can only be produced from the purest lead. Most lead contains copper, which, however, has no influence on the paint, as, in the process of manufacture, it is mostly removed. Among the different kinds of lead found in the trade, the American lead of Missouri stands at the head in regard to purity; next comes the lead of Steyermark, in Germany, and the English Bloquet lead. These three kinds of lead are very soft and exceedingly flexible. They serve for the manufacture of white-lead after the celebrated Holland method. The next qualities are those refined in the Rhenish province's. They are less flexible and contain more copper, besides some iron, antimonium, and silver, and produce a good white-lead, which, however, is not as white as that made from the preceding kinds of lead. After these kinds comes that of the Hartz Mountains, in Germany; and last, the Spanish lead, which is the worst of all, containing too much iron and antimonium. The Hartz lead gives, after the Holland method, a bluish gray, and the Spanish, a reddish yellow white-lead; and they are therefore only used for a first coat, and for mixing with other colors. As these inferior kinds of lead are comparatively much harder than the purer varieties, it is easy to distinguish one from the other by comparing the flexibility of plates rolled to the same thickness.
There are two principal methods of making white-lead. The oldest is that invented and practiced in Holland, and usually called the Dutch method. It requires a very pure material, as the result depends more on the quality of the lead employed than on the care in the manipulation. The newer method is of French invention, and in this, on the contrary, the result depends more on care in the manipulation than on the quality of the lead employed, as a very inferior lead may, after this method, produce a very pure white-lead.
Therefore when a manufacturer can only obtain inferior kinds, he should follow the French method in preference; while, when he has occasion to procure a pure lead at a reasonable price, as may be the result of local circumstances favorable to transportation of such a heavy article, he should operate according to the old Dutch method, as the lead thus manufactured commands always a higher price in the market; chiefly for reason of its having more body or covering better, so as to be much more economical to the practical consumer, and giving the dealer a wider margin for adulteration with the, cheap sulphate of baryta, chalk, etc. This adulteration is practical to such an extent that a pure white-lead, ground in oil, without additional mixture of zinc-white, baryta, or chalk, is an exceptional phenomenon in the market.
The methods of detecting these adulterations by chemical analysis is easy enough; but we find that, after all, the best test, which determines the practical value - which is the only thing with which the painter has to do - is to cover certain surfaces, say a square foot for each, with equal quantities of different paints, putting it in a rather thin layer, and then to judge of the comparative value by their appearance after drying.
In our next, we will commence the description of the different manipulations practiced in making paints from lead, in the same detailed style as we have done for chrome and copper in our former numbers.