Make a Press Moulded Bowl or Dish
Step-by-step instructions for clay beginners to use a press mould
Plaster press moulds can be used to start various projects or to produce multiples of any one design. Find out how to use one properly and how to fix basic problems.
Press moulds are fairly common in the clay studio. Made of plaster, these are hollow bowl or dish shapes and can be used to start various projects or to produce multiples of any one design.
As their name implies, press moulds are used to shape flexible clay sheets that are pressed into it. The inside of the form is then trimmed and decorated and the piece is left to dry until it is stiff enough to support its own shape and weight. It is then popped out of the mould for the exterior surface to be decorated and for finishing touches to be added.
Anyone who has ever rolled out pie crust or used a pie pan can use a press mould with finesse.
There is only one crucial thing to remember; plaster moulds dry clay out very rapidly, so once you start a piece, it is best to work quite quickly up until the time the piece is unmoulded. Do not wrap a work in progress in plastic to take a break because when you return to continue, you might be adding wet clay to much drier clay. This difference in dryness might cause cracks during firing.
Follow these instructions to make a basic press moulded bowl or dish. You will need:
- A plaster press mould
- Enough clay to cover the inside of the mould, and if you wish, a little extra for decoration. You’ll want to make sure that your clay is relatively moist for this project as drier clay will tend to crack when you try to ease it into the mould.
- 2 strips of wood of equal thickness to use as roller guides. Generally around ½ in (1 cm) will do. (Try and match the thickness of your clay sheet to the size and scale of the mould. Choose thicker guides for a larger mould and thinner guides for a smaller one).
- A rolling pin
- A damp sponge
- An old toothbrush
- Slip
- Wooden tools
- Plastic sheeting
- Metal kidney
- Rubber kidney
- Pin tool
- A wooden or plastic bat
1) Wedge the clay, then flatten with the rolling pin. Place a roller guide on each side of the mass and roll out a sheet of clay large enough to line the press mould. It is important to roll the clay sheet out to an even thickness. Try to resist making the sheet too thin. If possible, roll out more than one sheet and store the extra together with your leftover clay in plastic sheeting.
2) When rolling, remember to rotate the sheet of clay or switch the direction in which you roll every so often. This results ion clay that is evenly rolled out and relaxed.
3) Lift the clay sheet over the mould so it completely covers the mould, with the extra overlapping the rim.
4) Carefully ease the clay sheet into place, taking care not to create any air pockets. Do not push the clay into the mould as this will leave finger marks. Handle gently to avoid tearing.
5) Use a damp sponge to gently dab the clay to fit into the mould. Unless you are making a deliberate design choice, do not smooth the surface of the clay by using a wiping motion as this will expose the grog in the clay. Grog, once brought to the surface, will give the piece a rough texture and cannot be glazed over easily.
6) If you are using a square press mould, use the damp sponge to ease the clay into the corners using a dabbing motion. You may have to lift sections of the clay sheet to facilitate this and avoid distorting your work. Work around each corner until the clay fits comfortably into the mould.
7) If you tear the clay sheet or if your sheet is not large enough to cover the entire mould, simply use one of your backup sheets of clay to complete your piece, allowing an overlap of ½ in (1 cm) where the 2 pieces meet. Again, be careful not to trap any air. Use your fingers to thoroughly blend the overlapped sections together. It is important that the join be strong to avoid cracking later on. Then scrape away excess clay with a metal kidney, taking care not to remove too much clay (or you’ll find yourself back where you started and maybe even damage the mould). Finally, smooth the mend with a rubber kidney. You should end up with work that is of uniform thickness.
8) Trim off the excess clay lying outside the mould by using wooden tools (metal ones will damage the plaster and cause plaster debris to contaminate your piece). The best way is to use one of the wooden roller guides. Place the guide flush with the mould rim and use both hands to draw it towards yourself, taking the excess with it. Work around the rim and take away sections at a time to avoid distorting the clay.
9) When the excess clay has been removed, smooth the inner surface carefully with a rubber kidney. This will help compact the clay and help show off your glaze.
10) Decorate the inside surface of your piece if you wish and touch up the rim if necessary.
11) Then wait for the piece to dry. If you’re concerned that the rim is drying too quickly relative to the centre of the piece, wrap the entire thing loosely with plastic and leave the piece to dry slowly inside the mould. As a general rule, it is better to wait for the clay to dry slowly than to speed up the drying process and end up with a structurally weaker piece.
12) When the clay starts to shrink away from the sides of the mould, your work is ready to be removed. Put a bat over the top of the mould, then turn both over so the piece drops out onto the bat. This method minimizes the possibility of damage better than lifting the piece directly out of the mould. You are now working with the piece lying upside down on the bat.
13) If you had to join 2 pieces of clay before or had to fix a tear in your piece, now is the time to roll out a small coil and reinforce the join on the exterior of the piece. Press the coil into place along the join then blend it into place with a wooden tool. Finally, scrape away any excess clay carefully with a metal kidney.
14) If your clay is on the dry side, you may have to score and slurry to help the coil stick. To do this, moisten the old toothbrush and use it to roughen the surface where the coil is to go. Brush on some slip, then gently but firmly press the coil into place and blend it into place with a wooden tool. Finally, scrape away any excess carefully using a metal kidney.
15) Smooth the outside surface carefully with a rubber kidney (like you did for the inside). This will help compact the clay and help show off your glaze.
16) Make 3 balls of clay for a foot. Or roll a coil for a foot. Carefully decide on their position and mark this with a pin tool. Use the old toothbrush and some slip to attach the foot.
17) Add decorations to the outside of the work if you wish.
18) Turn the bowl or dish the right way up and finish the rim by smoothing out any rough edges with a rubber kidney.
19) Set the pot aside to dry until it is ready for firing.
If you don't have access to a plaster press mould, don't despair. Substitutes can be found around the house. See DIY Improvised Press Moulds for ideas and tips.
Curious for more? Please visit the article archives and e-mail me with your questions.
