Directly work is suspended the glass remaining in the crucibles is ladled into water, drained and dried.
The crucibles or pots used for the production of optical glass very closely resemble those used in the manufacture of flint glass for other purposes; they are " covered " and the molten materials are thus protected from the action of the furnace gases by the interposition of a wall of fireclay, but as crucibles for optical glass are used for only one fusion and are then broken up, they are not made so thick and heavy as those used in flint-glass making, since the latter remain in the furnace for many weeks.
On the other hand, the chemical and physical nature of the fireclays used in the manufacture of such crucibles requires careful attention in order to secure the best results.
Glass mixtures containing lead are melted in covered, beehive-shaped crucibles holding from 12 to 18 cwt.
In some works, the older method of melting the glass in large pots or crucibles is still adhered to, although the old-fashioned coal-fired furnaces have nearly everywhere given place to the use of producer gas and regenerators.