Plaster Bats And Drying Problems

[clay lover]

I used some new plaster bats yesterday, threw several 5lb bowls. this is the second time for using these commercially made bats. 1st time the bowls were thrown, covered same as if they were on regular bats, and 2-3 days later they released from the plaster bat, smooth as you know what on the bottem, and wonderfully easy to trim, no ragged edges to get past.

 

Today I went to the studio to check the bowls and they were already ready to come off the bats, I had set them on racks, where air could get to the bottom of the bat, but with the tops covered with double layers of old bed sheets, in a closed studio with no air , heat, ect. half of the bowl had shrunk in some way that had produced a bottom that looked like a trimmed foot ring! and had cracked along the "rim inner edge. Very wierd. Was this due to having air around the bottoms of the thick plaster bats? The worst cracking was on a bowl that had been made on a 'adapt-a-bat system bisqued tile insert, that I had lifted out of the square recessed bat to facilitate drying. Is "facilitate drying " the problem here??

 

 

Other thing I noticed about the plaster bats; when throwing, the excess water, slurry formed a dry rim around the bottom of the pot, making it hard for me to get to the bottom edge of the clay I am wanting to pull up. I stopped pulling several times and used a plastic square edged rib to carve away the dry clay, a ring around the bottom of the pot, out across the bat, and square up the bottom so I could get under it.

 

Any comments? do you use plaster bats, and why?

[Idaho Potter]

Plaster bats are my preference. I have some Jepson bats for large items, some Hydrostone for small items and homemade ones for all else. When I finish throwing a piece I wheel trim as close as possible and peel away the waste clay. I then cover the items loosely with plastic bags or lightweight sheeting and leave them until the pots pop off. Usually takes one to two days then turn items upside down to get the bottoms to trimming dryness.

I set my bats on lathe shelves so air can get around them--they get pretty soaked from throwing--otherwise it could take three days or more before the pots popped off the plaster. Your cracking could be because the rims dried faster than the foot, try using plastic rather than cotton sheets. Never had that happen so can't do more than guess.

 

The only thing to be careful with is the wheel trimming so you don't scratch into the plaster and accidently get plaster particles in your reclaimed clay.

 

I also had the "trimmed footring" look a couple of times and finally figured out it was me capturing air as I tried to adjust the size of the foot while throwing. Usually happened when I opened and after establishing a compressed base, tried to enlarge the base.

 

As to the dry slurry on the bat--is it just a skin of slip? If that's all it is, most of it will come off when you wheel trim and peel the heavier waste clay off, so I'd ignore it. Use your knuckle or fingertip to keep the clay at the base nudged up for lifting.