What’s this white fuzz on my plaster bats?

Yesterday I woke up to some strange fuzz on my plaster bats.

Crystals on plaster bat, white fuzz
Small amount of fuzz on the top left corner
Crystals on plaster bat, white fuzz
All along the middle
Crystals on plaster bat, white fuzz
Alternate angle of the thinner bat

These plaster bats are used during clay reclaim and thanks to the clayart forum, I soon discovered that the white crystal fuzz was probably soluable salt or Calcium Carbonate (yahoo! Neither are too dastardly).

And yes, I’ll quickly explain the reclaim process: All my excess clay – the offcuts, trimmings and the naughty vessels get put in a special reclaim bucket to soften up. I then put these slops on the plaster bats to dry out so that I reuse the clay, reducing material waste.

As the water is ‘sucked out’ of the clay by the plaster, the clay become more like play-doh, less like puddles of mud. Depending on how thick your bats are and how much clay you have drying out, this process can take a few hours or a day, even two.

Eventually, the plaster’s ability to dry out the clay is hampered and it says ‘I can’t drink anymore! Enough!’  Ha – I wish my plaster bats spoke to me but because plaster bats can’t talk, it starts creating little white fuzzy crystals to let us know it’s had enough. In technical terms, Calcium ions from the plaster is drawn out during the clay drying process and react to air (specifically the carbon dioxide) to form these crystallised structures after the clay is removed.

Tom Buck suggested that ‘sanding the surface…will rejuvenate a plaster form’ so I’ve decided to test that out as opposed to just wiping them off (as they’ll probably just grow back again right?).

I also decided to make a new plaster bat. I’ve wanted a thicker bat as my other two are quite small (used a plastic kitty litter box as the mold) which makes them easy to lift and transport but I want something a bit more heavy duty now that I’m set up. But I couldn’t find my TAFE notes. Ok,  I didn’t want to search through the boxes of uni/tafe stuff that are under my bed and get distracted by other things in other boxes so I decided to find a water:plaster ratio online and the ever helpful (and also distracting) Ceramic Arts Daily helped me out but I had to convert into ml and grams.

Water Plaster Ratio for Molds
My water(mls):plaster(grams) conversion table

After more reading on the Boral site (couldn’t help it, I was looking up the properties of their pottery plaster) I found that their recommended ratio had less water which would make the bats stronger but less porous.

Water plaster ratio for pottery plaster
Ratios for Boral’s Pottery Plaster

Long story short, I have one new super thick plaster bat and two freshly sanded thinner bats and I don’t have to get freaked out by white crystal fuzz in the studio again.

If you’ve had this issue and beaten it in a different way, please comment and let me know!!

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