Celina’s blog “On ceramics” :Forming, Slab Building

11 Forming. Slab building

This is a very imaginative way of forming and it is used in different ways:

Straight walled vessels

Flat plates, molded or otherwise

Piling up slabs so to make a volume

Tiles, of course!

Molded bowls and vessels

And a limitless forming possibilities.

The photography showsa 4 inches high slab buildt Yishin teapot The author collection

The most up to date way of making slabs is by using a pressing machine, but slabs can be made by many other methods: by cutting it with a wire guided by two wood sticks placed one opposite to the

other: the sticks are carved according the desired thickness of the slab. The

tensed wire fixed by the hands on those carvings should slip along the block of clay so each slab is cut even. A set of sticks placed in both sides guide also the wire, as illustrated in my book on ceramic throwing. A wood roller, similar to those used in bread making, can be used to press the clay guided by two sticks of the desired thickness placed to the left and to the right side of the clay and also, the clay can be padded with a flat board on the table to the desired thickness.

The slab forming method consists in: after making slabs of even thickness to cut them to the required shape and to glue their borders, one to the other, by way of slurry made out of the same clay used to make the slabs.

Obviously, fresh clay slabs cannot be freely manipulated unless they can keep their shape, this meaning that the slabs have to be let to dry a bit.

How much?

To determine the ideal hardness it is not free of difficulties.

When using leather-hard slabs (dry as to have the consistency of leather) and slurry is used to glue two pieces, it is without saying that the slurry will shrink more than the slabs and detach from them; if not when drying, inside the kiln, spoiling the work.

The usual way is to score the areas to be glued and to use thick slurry, as thick as possible, so the shrinking difference in drying between the walls and the glue does not produce crackles. Joints should be carefully pressed.

As hard as the slab is, as difficult is to succeed in gluing it. As soft as the slab is, as difficult is to succeed in obtaining an unblemished shape.

China’s Yishing potters, famous for their beautiful teapots, use thin leather hard slabs when molding them. They prefer a quite hard consistence in their clay, as hard as to need a pad to flatten it. By wisely calculating the quantity of clay they need for each part, they make a ball and pat it on the table with the help of a flat wood-made tool. A teapot is simply shaped either by padding the slab and forming the piece by hand or by using a mold to determine the final shape. Once they are satisfied with the thickness (one to 2 millimeters at most) they cut out the required shape and adapt it to the concavities of the mold, Their clay is finely grained; by way of polishing it with the help of a piece of man-made leather or similar, they render the clay almost impervious to water. Yishing teapots are not glazed and, when in use, they should never be washed with detergents but only with warm water, their light absorption index is the clue that explains why they keep the flavor of the tea for the best.

Here some hints when handling a clay slab.

~ As soon it is cut, place it on a flat un-varnished wood board where a piece of absorbent newspaper has already placed.

~ On top of the slab place another piece of paper and another board. Tap with a flat hand all around the top-board with measured strength to make sure that the slab is really even and flat.

	~ Take off the top board and the top paper. The paper beneath impedes the clay to stick on the boards.
	~ Let it dry to the most suitable hardness by placing over the slab a dry wood board to a distance of no more than 4 or 5 cm (use

small wood cubes or similar to sustain the top board). This is to keep the air around as stable as possible and allows for an even drying.

~ After a few hours, again place a new piece of paper and a board on top, and taking care of lightly pressing so the slab does not slip out, put all: boards and slab, upside down. Take off the board on the top together with the already humid and now corrugated newspaper.

~ Do this as many times as necessary until you judge it is enough stiff for you to work the final shape.

If you just leave the slab to dry without protection, the top surface will dry quicker than the surface beneath resulting in deformation. And this is also true for plates and other flat objects.

~ In the same way, when you need to displace the slab, do never lift it: it will deform! First of all, the new emplacement should be at the same level that the board: Pull the slab from the paper beneath, this way, the slab slips without changing its shape.

~ When building the vessel, handle the slab very carefully, so to avoid any undesirable change of shape.

~ Dry the finished piece very slowly, as slowly and even as possible.

Molded Yishin teapot 4.5 inches high from the author collection. Unfortunately I can not read the author name.

Celina would be pleased to try to answer any comments & questions related with her blog text, and when not able to do so, she gladly would go in quest for an answer among clay-people around.

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