MOLD: 4 Made with bars of wood
MOLDS – Building them up with bars of wood and clay
If you need a simple mold that will only be used a few times, then it is worth doing it yourself, but if it is going to be used a lot and you need 4 or 5 units of the same mold, or it consists of two or three pieces, then it is worthwhile having it made professionally.
The general rules for molds:
Place whatever you want to make a mold of onto a large, movable wooden board. Calculate where you want to put the outer walls, which can be built up either in wood or clay. The size and strength of the walls of the mold are in relation to the length, width and height of the object to be copied. The bigger the piece, the bigger and stronger the walls should be. When designing the object you want to make a mold of in clay, bear in mind that the clay will shrink by about 5% and ensure that the pieces will fit into your kiln.
Building with wood:
Needed: A wooden board to make the mold on, small planks of wood, clay, a large bucket, plaster of Paris and bleach.
Method: Build up the outer walls using the planks of wood. Put a thin layer of clay between all the parts that have to be joined and force them together. Fill up all joints, inside and outside, with clay, level them out and round off the corners. Before making the mold, paint the inside with bleach mixed with clay. This will make the separation of the plaster easier.
Building up with clay:
Needed: Plank of wood to make your mold on, battens, rolling pin, clay, large bucket and plaster of Paris.
Method: Roll out a slab of clay to the desired thickness, cut it into strips to the width needed for the height of the walls. Stand it up and put it round what you are going to make a mold of, leaving enough space, height and widthwise to form the mold. Join the ends of the wall when they meet. Put a coil of clay round the inside and outside where the different parts join, especially walls, floor and corners and push it in and round it off. This will strengthen and hold the walls in place and stop plaster from escaping underneath.
Plaster of Paris: Put water into a bucket and add the plaster, stirring all the time to get rid of lumps. In about 3 minutes it will start to thicken. When it gets to the right thickness and is like a thick heavy cream, pour it over the prepared clay. Let it spread round and up to the height of the walls, pouring slowly so it enters into all the small spaces and also to avoid putting too much pressure on the walls. When full, level out the top and leave it to dry.
To separate mold and clay: Take the walls off and turn it the right way up. Pull out the clay and when separated, wash and clean each part of the mold. Scrape off any bits of plaster that have run under the clay and formed rough edges. Name and number each piece clearly with paint.