In the sixteenth century, as a contemporary writer puts it, ‘_Tous les rois et princes désiraient et affectaient avoir en leurs royaumes cette science_’: that is to say, the knowledge of the methods of preparing the true _cristallo_. To obtain this knowledge from Murano was difficult and even dangerous. What wonder, then, that recourse was had to the Consuls of the glass-workers’ guild at L’Altare? These officials seem to have been always ready to negotiate for the supply to foreign princes, or even to private individuals—if the requisite payment was forthcoming—of one or more of their skilled gentleman glass-workers.[165] But in this case, too, a keen eye was kept upon these men: they were bound by the strictest oaths to practise their craft, when in foreign lands, with the greatest secrecy; above all they were forbidden to take any apprentices from the people among whom they were working. In France, where so many of these Altarists settled, these restrictions were the cause of constant friction, but so successfully were they as a rule enforced, that we find that, in the case of more than one centre of the new industry, it was necessary during a period of at least a century to have recourse from time to time to the original source at L’Altare, to replace the Italian workmen who had died or wandered off to other towns. For like their rivals from Murano, these Altarists were always on the move. We are reminded in this of the wandering porcelain ‘arcanists’ of the eighteenth century, who carried from one German court to another the secrets of their craft. To give but a single example; M. Schuermans has traced one of these _gentilshommes de verre_ in migrations that led him successively to London, Liége, Maestricht, Rouen, and Paris. In what respect, if in any, did the glass manufactured by these ‘licensed’ craftsmen from L’Altare, differ from that made by their rivals the ‘outlaws’ from Murano? This is a question that we are not in a position to answer. That there was some difference in style of working, and not merely in the technical excellence of the glass, would seem to be proved by the expression ‘_à la façon d’Altare_,’ or ‘_ad uso d’Altare_,’ so often applied to it. There is no doubt that the glass made ‘_à la façon de Venise_’ was, on the whole, regarded as of greater excellence, and that in the impossibility of obtaining workmen from Murano, the resort to the Consuls at L’Altare was in a measure a _pis aller_. We must not, however, as has sometimes been done, look upon the craftsmen from the latter town as incapable of producing anything of artistic merit. On the contrary, they not only turned out a true _cristallo_, but much of the enamelled glass that was so successfully made in France in the sixteenth and seventeenth centuries came in all probability from furnaces worked by Altarists.