The first board is then removed, and the pot maker begins to build the sides or walls of the pot upon the circular clay slab by working the clay in rolls around the circumference of the slab to a thickness of 3 in., which gives the thickness of the pot walls. As he works and presses on each roll with his right hand, he supports the inside of the curve with his left hand, and presses roll after roll around the circumference of the slab of clay, increasing the height of the walls until he attains a height of about 6 in. The height of this wall is increased by about 6 in. every other day or so; these time intervals allow each section built to stiffen a little before beginning upon the next section. The workman passes from one pot bottom to another, building up these sections until he builds each to a height of about 30 in., when he places within each pot a clay ring about 18 in. in diameter, which he has previously made.[3] After placing these rings within the pots, the pot maker begins to form the hood or dome of the pot by working on the clay rolls, and at the same time drawing the sides inwards towards the middle, lessening the thickness of the walls and gradually diminishing the open space until it is covered and sealed in. Whilst the clay is still soft, the mouth or working opening is worked on and cut out of the dome, and the whole finished and smoothed by means of wooden tools. Footnote 3: These rings, floating on the metal, are used by the glass makers to keep back the scum of the glass away from the middle portion from which he gathers. The pots are now completed and are left to dry gradually at a moderate heat, which is increased a little at the end of a few months in order to thoroughly dry them. They are then removed from the boards and are ready for the furnace. Crucible pots are made in a similar way, except that at the height of about 27 to 30 in. the pot maker finishes off the top edge of the walls and leaves it in that form to be dried. Many efforts have been made to manufacture pots by other methods. One which has been tried with a fair amount of success is to cast the whole pot or portions thereof by using a plaster case mould and pouring in liquid clay slip. Another method which has been tried is to press the form by means of a hydraulic press and mould. Other mechanical contrivances have been used, but few of them have given such satisfactory results as the hand-made pots. MIXTURE FOR POT-CLAY _By volume._ (=Base=) Fine ground strong 5 parts Fire-clay (=Binder=) Fine ground mild Plastic 4 parts Fire-clay (=Grog=) Ground burnt Chamotte 2 parts (=Grog=) Ground selected Potsherds 1/2 part