The print is soaked first in a solution of potash, and then in one of tartaric acid. This produces a perfect diffusion of crystals in bi-tartrate of potash, through the texture of the unprinted part of the paper. As this salt repels the oil, the ink-roller may now be passed over the surface, without transferring any of its contents to the paper, except in those parts to which the ink had been originally applied. The ink of the print prevents the saline matter from penetrating wherever it is present, and wherever there is no saline matter present the ink adheres; so that many impressions may be taken, as in lithography.