I reasoned from this that oil suffered a change from exposure to air, and by combining itself presumably with oxygen acquired a more earthy character. This deduction may be correct or not; but it led me to experiment with oil as a binder for various earthy substances, because I reasoned that such a composition would be insoluble in water. The only question, then, would be if despite the intermixed oil it would permit itself to be prepared, that is, if it could be made resistant to other fats.
The result justified my hopes so thoroughly that I am convinced now that with various compositions of clay, chalk, linseed oil, and metallic oxides a stone-like mass can be made that is excellent for coating paper, linen, wood, metal, etc., and thus for making plates that not only replace the stone for printing, but in many cases are far superior to it.
I shall give the world a book soon about these fortunate attempts of mine, and thus perhaps give expert chemists an opportunity to perfect my invention still more.
VII
CHEMICAL PRINT ON METAL PLATES
All metals have great inclination for fats; but if they are quite clean, being ground with pumice, for instance, or rubbed-down with chalk, they can be prepared like a stone, that is, they acquire the property of resisting oil color, thus becoming available for chemical printing.
Iron and zinc can be prepared like the stone with aquafortis and gum.
To prepare zinc and lead, aquafortis with nutgall and gum will serve, but a slight admixture of blue vitriol will make still a better preparation, and this in a degree that improves according to the amount of copper that the surface acquires from the coating. The most durable preparation for lead and zinc is a mixture of aquafortis, gum, and nitrate of copper.
Brass and copper are best prepared with aquafortis, gum, and nitrate of lime, all mixed in proper proportions.
Lime and gum are a good preparation for all metals; also potash with salt and gum.