DIY Network

Making a Mold and Extruding Clay Making a Mold and Extruding Clay From "Throwing Clay" episode DTHC-106

Basket making is one of the world's oldest crafts. Master potter Bill Van Gilder combines these two ancient crafts to make a handsome basket from stoneware clay. Bill, who has been throwing for more than 30 years, enjoys designing unique pieces of pottery.

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For this project, Bill will throw at the wheel and hand-build to create this eye-catching form (figure A). His inspiration for the piece is a traditional wooden fruit basket. He's changed the shape slightly to fit a clay mold, which he throws on the wheel, prior to creating the basket (figure B).

Figure A

Figure B

Tools:

25-lb. block of bagged clay
extruder
three (3) shaped dies
porous mold
rolling pin
two 3/8"-thick measuring sticks
ruler
fettling knife
small painter's trim roller
length of wooden dowel
banding wheel turntable
two small ware boards
water and a small sponge
brush
wax resist emulsion
glaze

Making a Clay Mold

1. Bill kneads and de-airs approximately 5 pounds of clay for the basket mold. For the mold, he can use any type of clay he has in the studio, as no special clays are required for this step (figure C).

2. The form is made on a bat; the bat allows it to be removed from the wheel head without distorting the shape. Bill keeps the clay wet as he centers and opens the form (figure D), leaving the base approximately 1/2" thick. He pulls the walls upward and inward (figure E).

Figure C

Figure D

Figure E

3. He splits the rim, creating a ledge at the top; the ledge will let him lift the mold, which is thrown wider at the top and more narrow at the bottom, out of the basket (figure F).

4. Excess clay is trimmed away with a sharp rib, and the outside surface is smoothed with a sponge. Smoothing the surface is important: any blemishes on the outside of the form will appear on the basket as the clay is pressed against the mold.

5. The walls of the form are thrown thick (not normal throwing practice for experienced potters) but important to the process here because they will absorb water from the basket clay while it is pressed against the clay (figure G).

Figure F

Figure G

6. When finished, the mold dries to a bone-dry consistency before being fired in the bisque kiln. After firing, the form will be very porous.

Extruding Clay

An extruder (figure H) is used to make the clay pieces used to build the basket. Extruders are the adult versions of fun factories used by children to mold clay into shapes. A handle forces a plunger down into the clay; the plunger then forces the clay through shaping discs, known as dies, and out the bottom of the extruder. A die tap evenly compresses the clay through the die, sending it out the exit barrel in a long strip (figure I).

Figure H

Figure I

	Figure J
	Figure K
	Figure L

Dies are easily made from 1/4" Masonite®. Three separate dies make up the cross-sections of each part of the basket. A flat-shaped die is used for the slats, an L-shaped die is used for the rim and an indented die is used for the handle (figure J).

The first piece to be extruded is the basket rim. Bill uses cooking spray to coat the inside of the exit barrel; the oil prevents the clay from sticking to the sides and makes for easier clean-up.

Processed clay is used straight out of the bag. Bill quarters the clay lengthwise and drops a section into the barrel, which holds approximately 10pounds of clay. The clay from the first die will need to wrap around from one handle to another, a measurement of approximately 28", based on the measurement of the mold.

Next he loads the flat die (figure K), used for the basket side slats. The basket is approximately 7" tall. Bill will add an inch or two at the top to accommodate his fingertips as he handles the slats, making each slat approximately 9" long. He loads another section of clay into the machine, extrudes six slats, then cuts them in half, creating 12 slats (figure L).

Because the handles are short, he needs to load only a small piece of clay for the third die. After extruding the handles, the parts are complete and ready to be fitted to the mold.

RESOURCES :

Kilns
L & L Kilns
Website: www.hotkilns.com

Clay
Highwater Clays
Website: www.highwaterclays.com

Extruders
American Art Clay Co. Inc. (AMACO)
Website: www.amaco.com