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testing for water absorption: standard clays 240 and axner's m=

updated wed 25 nov 09


Ron Roy on mon 23 nov 09

accabee Mix 5 Clay

Hi Miri,

Sorry to be so late with this - good for you for posting that test data - a
wonderful service to all those potters trying to make a decision that makes

Most Clay companies don't test each batch of clay so you should test each
batch as you buy it to make sure it has not drifted.

I tested some of Tom Colemans porcelain - supposed to be good from cone 6 t=
9 I think. Did two firings - two different batches - one at 6 half down and
one with 7 starting - both have low absorbency - like 0.1 to 0.4 so i
thought they would hold water. Not so - three cylinders form each batch and
each firing - filled with water overnight - paper wrinkled under all

I cannot explain how the water got though any clay with that low absorption
- perhaps the secret ingredient?

Best regards - RR

On Wed, Oct 28, 2009 at 12:07 PM, Miri Hardy wrote:

> In addition to glaze testing, I've been testing two clay bodies for glaze
> fit, general usability (such as throw-ability) and glaze
> absorption.
> The two clays I've tested are both C/6 white stoneware bodies: Standard
> Clays 240 and Axner's Maccabee Mix 5 Clay (WC-
> 901). .
> Detailed information about my experience so far with the two clays is
> available here:
> The reader's digest version of my findings:
> I conducted water absorption tests as outlined in John Hesselberth and Ro=
> Roy's Mastering Cone 6 Glazes. I repeated the
> test three times (3 different firings, different batches of clay) for eac=
> clay.
> The test results for the Axner Maccabee ranged from 1.02% to 1.77% (avera=
> =3D3D 1.42%)
> The test results for the Standard 240 ranged from 4.00% to 4.52% (average=
> 4.33%)
> In their book, John Hesselberth and Ron Roy recommend confirming that wat=
> absorption for one=3D92s fired clay is no higher than
> 3% and preferably 1-2%. Considering my results (and some random cracking=
> I don't think I'll be ordering any more of the S-
> 240....
> All the best,
> Miri in PR

Ron Roy
15084 Little Lake Road
Brighton, Ontario, Canada
K0K 1H0