[Clayart] clay for glazes

vpitelka at dtccom.net vpitelka at dtccom.net
Tue Oct 4 00:41:20 UTC 2022

Hi Ron - 
I experienced exactly that result in replacing some kaolin with ball clay in
a glaze recipe out in California, but it was on purpose and it did exactly
what I wanted.  In undergrad school at Humboldt, we had a glaze called
"Mutton Fat."  Yeah, doesn't sound very exciting.  But I liked it over slip
decoration.  But as certain materials became obsolete and I substituted
newer equivalents, Mutton Fat went partially opaque.  I tried to take the
easy way out and consulted the glaze chemist at one of the leading West
Coast clay and glaze suppliers.  I followed his instructions, and the glaze
went in the opposite direction, becoming almost completely opaque.  At that
point I got out my books and studied up, and all it took was replacing some
of the kaolin with ball clay.  I ended up with a nice cone-10 satin clear,
and used it in my studio, Railroad Stoneware, for ten years.  
- Vince

Vince Pitelka
Potter, Writer, Teacher
Chapel Hill, NC
vpitelka at dtccom.net

-----Original Message-----
From: Clayart <clayart-bounces at lists.clayartworld.com> On Behalf Of
ronroy at ca.inter.net
Sent: Monday, October 3, 2022 2:22 PM
To: Clayart international pottery discussion forum
<clayart at lists.clayartworld.com>; mel jacobson <melpots at mail.com>
Cc: clay art <clayart at lists.clayartworld.com>
Subject: Re: [Clayart] clay for glazes

In many cases a straight substitution of ball clay for kaolin will NOT
result in the same looking glaze. Ball clay always has more silica and less
alumina than any kaolin.

If you use the same amount of ball clay to replace kaolin you get more
silica and less alumina. Depending on how much kaolin is replaced you can
turn a matte or semi matte glaze into a shiny glaze.

This glaze obeys all the "rules" we list in our book for making a stable
liner glaze. The expansion is right for a good fit on most clay bodies.  If
colouring oxides are used and it's slow cooled it can resemble a high fired
reduction glaze.

C6 Glaze #1RR with kaolin.

Frit 3134 - 20.0
Dolomite - 10.0
Wollastonite - 10.0
Feldspar (Min spar) - 20.0
EPK - 20.0
Silica - 20.0
Total - 100.0

The same glaze with the right amount of ball clay substituted to get the
same amount of alumina and silica. If you can't get SGP#1 ball clay I can
probably recalculate for just about any other ball clay.

C6 Glaze #2RR with ball clay

Frit 3134 - 20.0
Dolomite - 9.5
Wollastonite - 10.0
Feldspar (Min spar) - 17.5
SGP ball clay - 29.5
Silica - 13.5
Total - 100.0

Those glazes with less than 10% kaolin can benefit from subbing in Ball clay
for kaolin. This will improve suspension on the bucket and stop powdering of
dry glaze on pots. Because ball clays have more iron in them compared to
kaolins you may notice some slight change in colours - especially with a
white glaze.

If anyone fires either of the above glazes I would like to hear how they
work - thanks - RR

Quoting mel jacobson <melpots at mail.com>:

> For years we have seemed to always use EPK Kaolin for all our glaze 
> needs. It was the standard.
> A couple of years back I was having trouble with some of my standard 
> glazes cracking up during drying....and glaze falling off.  This was 
> new to me, and made me crabby.
> Ron Roy came to my rescue and suggested I use ball clay, half an half 
> with all my glazes as EPK has changed.
> It worked like a dream.
> While making 5x20 glaze here at the farm...I ran out of epk.
> So, I used full om ball clay.  It worked fine, I could tell no 
> difference.  5x20 dries like cement on my pots...esp when placed in 
> the sun.
> ( it is about 3/4 of a block to my kiln from my deck where I glaze.
> I use my garden tractor with big baskets attacked and haul my 
> glazeware to the kiln. I drive the baby tractor right to the mouth of the
> Having a glaze that dries hard is a `god send`.)  I use a huge pile of 
> towels to wrap the pots loosely.
> So.....I have been thinking of using Redart clay in my 5x20 glaze.
> (I know it is earthenware and may flux some.)
> I would love clayarters to discuss clay bodies for glaze, how it 
> works, why it works, and variations of different clay.  I know it 
> would be of interest to most new clay workers.  ( and me) mel
> website: www.melpots.com
> www.melpots.com/CLAYART.HTML

Ron Roy
ronroy at ca.inter.net
Web page ronroy.net

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