Josiah Warren's 1830 "Reduction in the Cost of Printing Apparatus" described one of his attempts to make the power of the press widely available. An 1846 patent (#4479) issued for "Improvement in Compositions for Stereotype-Plates" marked on advance in this project. Matrices of a composite material, largely made up of clay, took the place of the lead matrices proposed in 1830 (themselves an improvement of copper matrices, in terms of the ease with which they could be used. (There is a reissue on file for either 1853 or 1883.)
It took me quite awhile to actually find this patent, although I knew roughly when it was issued. That's no big surprise, I guess, since the author of the reissue is listed as " JOSIAH WAEEEET," with an issue date of "Apr 25, 1346." On the positive side, Google Patents is now allowing you to download pdfs of the patents, after having recently made it impossible to even download page images efficiently.