At the moment I throw all of my work on wooden batts secured to my wheel with a pad of clay. Some are made from marine ply and others from moisture resistant MDF. Both work really well but over the past few months I have been researching throwing on plaster – I understand it can help with more even drying and removes the need for wiring off. I’ve had a few large pieces with wide bases crack during biscuit firing recently, possibly as a result of drying too fast. I’d also like to start making plates shortly, so I’ve been making some home made batts over the past few weeks to test them out.
First I needed a suitable mould… I was about to try and work out how to rig something up at home when I found the perfect tea tray, approximately 28cm in diameter and 2cm deep. My wheel does not have batt pins so using the tray was straightforward. I know that special moulds are available in the US that you can attach to your wheel so that every batt you make fits the pins accurately. Alternatively you can make batts the way I have described below and then, using a template, carve out the holes required for your pins.
Then I mixed up some potter’s plaster. To make a rough estimate of how much liquid was needed I filled the tray with water and then transferred it to a jug. I then poured a little away to allow for the increase of volume when adding the plaster. You need to sprinkle a little paster evenly over the surface of the water at a time, allowing it to sink, before adding more. When the powder no longer sinks and little peaks form you have the correct proportions. Using your hand stir the mix until you get a smooth thickening consistency without allowing your hand to break the surface. This helps to stop getting bubbles in the mix. Quickly pour the plaster into the mould and then tap the mould sharply on the floor or table to help raise any remaining air bubbles to the surface, then put the mould aside somewhere flat to cure. Do not wash waste plaster down the sink as it will block your drains. Let it dry on your hands and in the mixing bowl before chipping it off straight into the bin. It was at this point I realised that I should have greased the edges of the mould! The first batt was pretty difficult to remove, but using vaseline around the inside edge the second time was a massive improvement.
The batts take a long time to dry fully. I tested one the other day and threw a number of pieces today on some others. I worked out a few things along the way… It really helps to use very moist clay for the pad on the wheel. Before adding the batt wet it very thoroughly with slurry on the base – much more than you would with a wooden batt as the plaster sucks away so much of the moisture immediately. Don’t forget to use wooden tools as metal ones with damage the delicate and smooth surface of the batt. Also you don’t want to get any chips of plaster in your clay, as this can cause havoc when firing.
Following further research I understand the best plaster to use for batts is Hydrocal or a mix of 80% fine casting plaster and 20% herculite plaster. This is supposed to be more durable and lighter than normal potters plaster. I’m pretty pleased with my initial efforts… if they prove to be a success I will make some more with this stronger combination.