Double doors are provided at the entrance, with a porch, so as to prevent sudden inrushes of cold air and prevent draughts in the pot-making room. All unauthorised persons are prohibited entrance, and only those who work therein are allowed free access. They are made responsible for keeping the place clean, as well as looking after the clay and taking care of the pots whilst they are being made. The usual shape of a pot is of round section, 38 in. in diameter and 42 in. high, but many other shapes and sizes are used, according to the class of goods being manufactured. Thus, for colours, a very much smaller pot, less than one-third this size, is used, three of them, taking the position of one large pot, being set within one arch. For sheet and optical glass, a covered pot with a very large mouth or working opening is used. In some instances, as in the Hermansen furnace, the pots are oval or egg-shaped. These are used on account of their larger capacity in relation to the space occupied in the furnace. Other pots have an interior division, which has a syphonic refining action upon the glass; such pots permit of continuous melting and working, instead of the intermittent process adopted when the regular or common shape is used. For plate glass, open crucible or bowl-shaped pots are used. In regard to the manner in which the pots are made, and their subsequent treatment in annealing, the utmost care and control is necessary. In making the pots, the pot maker begins by making the pot bottom first, working the plastic clay paste into rolls about the size of a large sausage. He takes these rolls and applies them one after another in a circular form upon a round level board, the size of the bottom of the pot. This board is supported on a low table. As he applies each roll, he presses them together to exclude all air spaces between them, and continuously work the rolls on the top of each other in circles, until he gets a circular flat slab of clay in thickness about 4 in. and the width of the pot bottom. He then has the necessary thickness and size of the pot bottom formed as a clay slab, which is smoothed and leveled over the face with a knife or straight piece of wood. The slab of clay is then reversed upon another board, covered with a strong hurden cloth and a layer of ground-burnt clay, which prevents the clay from sticking to the board, and facilitates drying of the pots.