[Rockhopper]

(Another question spun from my experiments with locally dug clay)

I'm working with clay dug from a local creek and am finding that the clay has a lot of limestone in it (no big surprise here in SW Ohio). I've strained the clay through a nylon paint-strainer (not sure what the mesh is, but it's MUCH finer than the typical window-screen I've seen recommended by various websites) - removing nearly all of the sand. Several days after bisque-firing (^04-^06), I start seeing tiny white specs - in the 1/2 mm range - some of which are causing chips to flake off of the piece. (My clay actually looks very much like that in image #3 of Jeff Zamek's article: http://ceramicartsda...06/limepops.pdf - except I'm not seeing 'nodules' that large.)


Adding vinegar to the clay would turn the limestone (calcium carbonate) into calcium acetate. Am wondering if anyone knows whether calcium in that form would still turn into the white 'plaster' particles that cause lime-popping ?

I've read various articles that mention adding vinegar to clay to improve plasticity - and speed 'aging' - but I would be using a lot more in order to break down the limestone.

[Marcia Selsor]

Funny you should mention this, since last night I was cleaning some old calcium deposits from my water system prior to a new filtering system. I used a lot of vinegar.
It did soften the calcium but I still had to scrape.

Marcia

[Ben]

I'd try washing the clay.
Make it into a slip with LOTS of water. Thinner than whole milk.
Let settle 2 hours and pour off the suspended particles. Dry this and process in to test tiles.
repeat the stir and settle routine but wait less time (2hrs, 1hr, 1/2 hr, etc)

See if there is a certain waiting time that will settle out the limestone particles. This has worked for me with creek bank clays contaminated with limestone


As an alternative it is possible to grind the stuff until the pieces are so small that they aren't a problem. Of course, you'll have to have access to a ball mill to do that and most of us don't.