The first watches, the "Eggs of Nuremberg," were oval in shape, and had glasses which had been cut on a stone from a solid block of crystal. Later, when the watches took a round shape, this costly process was again used for the best watches, but for the inferior ones glasses were obtained by cutting, with a red-hot ring, two caps in small spheres of blown glass, the edges being trimmed on a grindstone. As the mechanism of watches lost its bulk, these glasses were found too protuberant, and again glasses cut in the mill from crystal blocks were used; these "cheves" glasses were very expensive. An attempt to reduce the cost was made by blowing small phials whose bases affected the form of the desired glasses. This foundation was separated, and its edges were finished on the millstone. But it was necessary to blow as many phials as glasses, and the price remained high. The modern manufacture of watch glasses differs from the early methods only in the perfection of its tools and better division of the work, but the principle has not altered. A tube has its end dipped in the glass pot and a workman blows a small bulb; this is softened by holding it near the door of the furnace, and, the end of the tube being put into communication with a reservoir of compressed air, a big sphere is blown.

This sphere, about 1 yd. in diameter, must be produced without rents, and must be of the requisite thickness. From it are cut convex discs of the size required. Formerly, this was done by marking round a metal template with the end of an earthenware tube at white heat; cold water being thrown over the glass, the sudden contraction of the cold material detached the disc. The modern method is to use a "tournette," which is a compass having a diamond as its marking point, its use is delicate work. The diamond having traced the circle, the latter is struck on both of its sides with a stick so that it may be detached. Using this disc as a template, the succeeding glasses are obtained very easily. The circles which are cut out touch each other, and leave as waste only the very smallest possible quantity. An able workman will cut 6,000 glasses a day. After the separation, the glasses are in the form of more or less concave discs, following the shape of the sphere from which they were cut. Their edges require to be deepened for the purpose of raising them sufficiently over the surface of the dial to leave a free circulation for the hands. One way of doing this is to place the discs over moulds of fine earth containing a receptacle of the form which the glass is desired to take.

These moulds are thrust in an oven, and when the glass is softened by the heat a workman with a plug of paper forces down the glass into the receptacle. After this operation, it is necessary to polish the whole of the glass on a stone; but, to avoid this, a different moulding process may be used. The glass is placed over a mould of the same kind, but of convex form, and of such dimensions that the edges of the disc pass all round it. In softening it in the oven, the sides fall the length of the mould; a workman completes the operation by capping the mould with a wood model. The edges are bevelle 1 on a grindstone and polished on another stone. For costly watches thick glasses are made, and from these the outside convexity is ground off, leaving a flat surface; such glasses are known as " flettage "; from some the central part only of the convexity is removed; these are known as " pointillage."