But this process of drawing designs with a diamond point on the surface of glass required the sure hand of an artist; there was no room for any ‘_pentimenti_’—moreover, the result was not effective.[206] Before long, in Germany at least, except here and there by amateurs, it came to be used merely as supplementary to the newly introduced processes of cutting, engraving, and polishing—that is to say, to the combination of methods concisely indicated by the Germans as _schliff und schnitt_. This was, indeed, a return to a very old treatment of the material much in favour in later Roman times. We have recognised in the so-called Hedwig glasses the last efforts of an art already extinct in the West and decadent in the East; but we have no link with which to connect these rude, deeply carved goblets with the engraved glass of the German renaissance. The Germans were, indeed, familiar with the processes employed in polishing the surfaces of hard stones, especially of their native agates (as in the Hunsrück district). This they effected in early days by rubbing on a board, the _schleif-platte_, and already by the middle of the fifteenth century by means of a grindstone (_schleif-stein_) turned by water-power. There is, however, no evidence to connect this industry with the new art of engraving glass, which arose, it would seem, full-fledged at Prague and at Nuremberg just before the commencement of the seventeenth century.[207] There is, indeed, every reason to accept the origin of this art given by contemporary writers—that it was learned from the Italian carvers of rock crystal, who in the last years of the sixteenth century were working for the Emperor Rudolph II., that moody recluse and most unsatisfactory ruler, who was, however, an eager and industrious inquirer into all the new arts and sciences of the day. This essentially _cinquecento_ art of carving in rock crystal had been before this time carried to great perfection in the north of Italy. The most famous master was Valerio Belli (1479-1546), called Vicentino, from his birthplace. The finest work of this school is to be found in the caskets built up with plates of rock-crystal delicately carved in shallow intaglio.[208] Other artists carved in the round bowls and vases in the form of shells or other shapes, suggested, in the first place, by the outline of the original mass of crystal. If these men were in any way indebted to Greek artists from Constantinople or elsewhere, it can only have been for the knowledge of the mechanical processes, for there is no trace of Byzantine influence in their art. To judge by surviving examples, it was in the main the work carved in the round that found favour at the court of Rudolph II. We hear especially of two craftsmen from Milan, Girolamo and Caspare Miseroni, who worked for that prince.