[Clayart] Grog or course fire clay
vpitelka at dtccom.net
Sat Aug 18 20:12:33 EDT 2018
Bryan's advice is good, because boxed clays that contain soda spars sometimes become mildly deflocculated over time, rendering them pretty useless unless the chemistry is readjusted. Just a few drops of the saturated Epsom salt solution thoroughly wedged into the clay should make a big difference. I love the concept of "standupedness," and sand or grog in the clay are certainly the most common way of achieving that desirable quality in throwing. I just taught a teapot workshop in Chico, CA, and the clay provided was cone-10 B-mix with grog. It contained very fine grog, probably Kyanite or Mullite, and it threw like a dream. But I was just throwing teapots and not anything large.
Lubrication provided by water makes clay plastic, but friction between particles is also essential for structure during throwing or handbuilding. It's a fine balance. Too much water and the clay slumps. Too little water and it is stiff and unworkable. Sand or grog does not interfere with plasticity, but it does interfere with movement in a positive way, helping the clay to hold its shape.
Retired Faculty, Appalachian Center for Craft
School of Art, Craft & Design, Tennessee Tech University
Now residing Chapel Hill, NC 27516
vpitelka at dtccom.net
From: Clayart [mailto:clayart-bounces at lists.clayartworld.com] On Behalf Of Bryan Johnson
Sent: Saturday, August 18, 2018 1:12 PM
To: Clayart international pottery discussion forum <clayart at lists.clayartworld.com>
Subject: Re: [Clayart] Grog or course fire clay
Have you tried adding some Epsom salts? Make a saturated solution and add few drops in a lump and wedge, or about a pint par 300 pounds and pug or remix.
On Sat, Aug 18, 2018 at 6:01 AM Rod Haaland <rod.haaland at gmail.com> wrote:
> Folks. I've been on a quest to formulate a good clay body that can be
> thrown thin and stays put. I've tried several different "boxed" clays.
> All seem to be really flabby with a bunch of grog thrown in. I think
> it's better to get that "toothy" plastic strength from course fire clay. So...
> I'm opening the floor for a discussion of the best combination of
> clays for plasticity AND the ability to be thrown thin and maintain
> shape - I'll call it "standupedness".
> Rod Haaland
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