Bisque is a great alternative method for making hump moulds for those who don’t like – or don’t have the facilities for – working with plaster. A plaster hump mould is used here to make the bisque mould, but you could use an upturned bowl as an alternative, providing it does not have a footring. Also, this is a mould with a decorative surface design, which means you can only make this style of bowl from this mould – if you want a plain mould for more flexibility, simply leave out the impressed detail.
You will need:
Clay – any type will do although it would be wasteful to use your best or expensive clay because it will only be fired to bisque – inexpensive school-type clay is perfectly acceptable for these moulds
Stamps to impress your design into the surface – wooden, plaster or clay – homemade or bought
Hump mould – a plaster mould in a bowl shape, or a footless bowl you like the shape of
Before you begin:
If using a bowl to form your mould, first cover it with cling film to make sure the clay doesn’t stick to the surface.
Roll a slab of clay on a sheet of plastic – the slab must be large enough to cover your mould or bowl and at least 10mm thick.
Sit the mould or bowl on a whirler (or potter’s wheel), and carefully drape the slab over the surface.
Remove the plastic and smooth over the surface of the clay with a rubber kidney.
Holding your potter’s knife level with the bottom of the mould or bowl, neatly cut away the surplus clay at the base.
Work around the rim again with a sharper knife to remove burrs and refine the cut edge.
Centre the mould on a whirler then using a potter’s pin, rib or pointed tool, score a line about 10cm from the rim of the clay (at what will be the rim when turned the right way up).
Using your chosen stamps, impress a design around the circumference of the dish inside the scored line and rim but leave the centre free.
With the mould still centred on your whirler, rotate the mould and gently cut a shallow spiral with a loop tool, wooden or metal rib. This feature will allow the glaze to pool deliciously when fired.
Smooth over the spiral with a finger then carefully stamp any more detail you might like to add to complete the design. You may need to re-cut the base (rim line) at this stage because it will have distorted slightly when the clay was impressed.
Score a second line about 1cm from the rim, taking care not to spoil the impressed design.
Allow the mould to firm up to a point where it can be handled without distorting the shape.
Roll another slab of clay for the underside of the mould and allow it to firm up to the same degree as the bowl part.
Now carefully lift the bowl off the mould and position it on the slab of clay. Score around the mould to mark its position on the slab, then carefully remove it again and return it to the mould temporarily.
Cut out the base circle slightly larger than the marked outline; this will give you the flexibility to make corrections if the bowl distorts slightly in handling later, when fitting the two parts together.
Score the rim of the bowl and corresponding position on the slab – apply slip to both the areas to be joined and fit the two parts together.
Apply firm pressure to the bowl part of the mould to make sure the two sections fix together and that the bowl is perfectly round.
Cut away the excess clay around the base of the mould with a sharp knife then smooth over the join carefully with a kidney or scraper to neaten it up.
When the clay has firmed up enough to handle easily, turn the shape over and carefully cut out a circle in the base, large enough to fit two fingers inside – this will allow for easy lifting after making the actual bowl.
Allow the finished mould to dry slowly before bisque firing.
The bisque-fired mould.