The Venetians eventually redeveloped the skills of the Romans, and their secrets were so much sought after that regulations were passed forbidding the emigration of workers. The glassworks, said to be more than a half milelong, was moved in its entirety to the island of Murano in 1291 because of the fires it had caused. The glass produced was soda-lime glass, satisfactory for most purposes because it was very stable chemically and of practical hardness. Its moderate softening temperature made it very workable, and it could be resoftened a number of times if necessary to complete an article.The materials needed for soda-lime glass manufacturing were plentiful: sand and limestone were abundant, and soda ash was readily obtainable from the hardwood forests that also provided fuel for the furnaces. Desirable but scarcer materials included potash, produced by burning seaweed and favored by the Venetians more than soda ash, along with crushed river pebbles (selected for their whiteness), which most Italian glassmakers preferred to common sand.