All these branches of glassmaking were therefore practised by the Spaniards from an early period of their history. This people were also familiar with the use of emery powder, of talc applied to covering windows, and of rock crystal. We read in the translation of Abolais that crystal at that time was "found in many parts, albeit the finest is that of Ethiopia. The substance which composes it is frozen water, petrified. And the proof of this is that when it is broken, small grains are discovered to be within, that made their entry as it was becoming stone (crystallizing); or again, in some of it is found what seems to be clear water. And it possesses two qualities in which it is distinct from every other stone: for when crystal is heated it receiveth any colouring that is applied to it, and is wrought with greater ease, besides being melted by fire; insomuch that it can be made into any shape desired; and if this shape be round, and the stone be set in the sun, it burneth anything inflammable that be set before it: yet does it not effect this by any virtue of its own, but by _the clearness of its substance_, and by the sunbeams which beat upon it, and by the roundness of its form." We seem to foreshadow here, clearly enough, the application of this substance to making glasses to assist the sight, especially when the author of the treatise adds that on looking through the crystal, the human eye discovers "details of the greatest beauty, and things that are secreted from the simple (_i.e._ the unaided) vision." Rico y Sinobas (who possessed a fine collection of antique glass, Spanish and non-Spanish) inclined to think that in the time of the Romans the finest and strongest glass, as well as the costliest and the most sought after, was that which was manufactured in Spain. In early times the chief centres of Spanish glass-making were situated in the heart of the Peninsula (where now is New Castile), in the neighbourhood of Tortosa, and in certain districts lying between the Pyrenees and the coast of Cataluña, though subsequently the practice of this craft extended through the kingdoms of Valencia and Murcia, and the valleys of Ollería, Salinas, Busot, and the Rio Almanzora, forming a zone which reached from Cape Creus to Cape Gata. Other regions in which the craft was introduced, apparently at a later epoch, were those of the Mediterranean littoral, Cuenca, Toledo, Avila, Segovia, and other parts of New Castile, as far as the slopes of the Sierra de Guadarrama. In the rest of the Peninsula there is not the slightest indication (excepting an obscure reference by Strabo, to vessels and receptacles of _wax_) that glass was made during the Roman domination of the country, either in Andalusia, Lusitania (Portugal), or in the northern regions of Cantabria.