Technical Tips And SLIP Product Information CASTING #04 SLIP PREPARATION – COMMERCIAL SLIP • Sit the mould for an appropriate time until the firm slip (cast) forms up on the inside walls of • Ensure the slip is thoroughly stirred using the mould (approx. 30 minutes). Casting times a long stick at least 1” wide (paddle) for vary according to weather, mould condition etc. approx. 4 minutes. • Empty excess slip out of the mould into the • Always stir to the bottom of the bucket. original slip bucket (preferably through a • Ensure your slip is the correct type 30-40# sieve). (earthenware, stoneware, mid-fire, • Invert the mould to drain at an angle. porcelain, terracotta) • Approximately 1 hour later, turn the mould up • Stinky/Smelly is desirable for plasticity but the and use a plastic picnic knife to trim the “spare” odour can be masked with a little household (excess clay at the top of the mould shape). Do bleach (25ml/per 10L bucket of slip). not use a metal knife because you will damage • Ensure that no “clags” of leather hard, dry slip the mould. go back into the casting bucket. • Take the bands/straps off the mould, lie the • Always keep lid on the bucket when not in use mould on one side, carefully lift off the top – even during casting. half of the mould evenly without ripping the cast apart. MOULD PREPARATION • Keep the cast sitting in half of the mould for a • New moulds should initially be sponged lightly further 15 minutes before completely removing before use. the cast from the mould. • All moulds must be completely dry before use. • Re-band/strap the mould and continue casting • If older moulds develop white fur, it should or keep mould parts separate to dry until be brushed off with a dry, coarse paintbrush next use. before casting. • The “face” of each mould should be perfectly CLEANUP clean (free of old clay, dust etc.) – sponge if • “Fettle” (trim) the joins off the cast to remove necessary (the day before casting). the “seams” – a metal bladed knife is fine • Place mould sections together, strap and hold for this. up to the light – if you can see the daylight, • Trim the “spare” (excess) at the opening to the the mould is not properly fitted together cast to achieve a suitable even finish. (check for stray bits of clay on the locking • Sponge “seams” and “spare” using clean water devices “natches”). and small sponge till smooth. • Each mould has a life of approx 100 casts. • Allow to dry as for any other pottery item. Past this, they will lose detail and the • If using 2 different temperatures/types of seams enlarge. casting slip, it’s a good idea to colour one with food colouring to identify them. It can also help CASTING if each piece has E/W, S/W, M/F etc. engraved • Place all prepared moulds on a bench. Take on the bottom. a large jug and pour casting slip into the jug • Glaze and decorate as appropriate for the (rather than dipping the jug into the bucket). slip type. • Fill the mould by pouring the casting slip slowly into the bottom (not down the walls). Top up till meniscus forms. northcotepotterysuppllies.com.au © Northcote Pottery Supplies.