It is sometimes necessary to glaze large pieces with a brush, putting on several coats in order to cover the surface with an even thickness. The matt glaze requires a greater thickness than the bright glaze in order to develop its characteristic velvety texture. The greater thickness may be easily secured, because it flows more slowly than the thinner bright glaze and is less likely to drip from the sides of the piece to which it is being applied; but, on the other hand, it is at a disadvantage in that it does not, in flowing slowly, correct inequalities of thickness so readily as the more mobile bright glaze does. A certain thickness, however, is essential; and if, after firing, it is found that the glaze was put on too thin, a second coat may be applied and the article again fired.
_Firing the Glaze._--Before the glazed piece is fired the glaze should be dried and what runs down and collects about the bottom or foot should be scraped off. It should then be set in the kiln on a kind of pointed tripod of hard burned clay, called the "stilt," which prevents the glaze from sticking to the floor or shelves of the kiln. All glazed ware should be placed in the kiln with at least 1/2 an inch of space between the pieces to prevent them from sticking together during the fusing state of the glaze, when it is apt to bubble or "boil."
The firing of glaze is a process very similar to that employed in the production of bisque, already described. Greater care, however, must be taken in controlling the increase in temperature so that it shall be even and steady--free from all sudden flashes of heat. The cooling also should be very gradual and, as in bisque firing, the kiln should be allowed to get cool before it is opened. With this second firing the pottery is finished unless it should happen that a second coat of glaze is found to be necessary. If only a few spots need attention, this second coat is best applied with a brush.
The tools required for making this vase are the same as those used for the bowl, and the process of building is much the same. The chief difference is that it is more difficult to preserve the profile in building because the added height and the greater weight tend to bulge the lower part. To meet this difficulty it will be necessary to set the work aside quite often in order to let the lower part harden sufficiently to support the upper part.