[Clayart] Screening glaze mix

Michael Wendt mwendt at wendtpottery.com
Tue Oct 9 21:46:02 EDT 2018

Joseph, exactly right!
Early on it became policy in my studio that glazes would be stirred for a 
certain amount of time, then checked to see if there was any hard pan in the 
bottom of the bucket.
In particular, I make a silky tan mat glaze Toshiko white mat 9.9 LBS 
Custer, 7.7 LBS Helmer airfloat, 4.4 LBS dolomite) which melts at cone 10. 
To it, I added 10 % Superpax and 5 % Titanium Dioxide. It was first screened 
to 100 mesh and then 30 mesh Lewiston Hill Grit ( a local very high iron 
volcanic rock some call scoria) which created a beautiful speckled effect.
After several uses, I noticed the color and speckling had shcanged. Upon 
observing people mix it, I noticed they were mixing far shorter times than I 
taught them and they were not checkeing to see that all the settled material 
was suspended.
We had to toss several gallons because they were too far off color to match 
existing sets.
Oncce they resumed following procedure, the glaze worked the way it was 
supposed to work.
We always screen to at least 30 mesh each time to beat the bisque shard 
problem that eventually shows up.
Michael Wendt
----- Original Message ----- 
From: "Joseph Herbert" <josephherbert827 at gmail.com>
To: <clayart at lists.clayartworld.com>
Sent: Wednesday, October 03, 2018 6:46 PM
Subject: [Clayart] Screening glaze mix

> Complaints about working conditions in shared spaces aren’t met with much
> sympathy, rightfully so, I suppose.  A more or less constant condition at
> the 19 shared spaces I have worked in across the country is bisque
> particles in the glaze slurry.
> The pattern of adding a newly mixed batch of glaze to an existing bucket,
> without screening the existing material, preserves the collection of 
> bisque
> particles at the bottom of the bucket for re-suspense and random
> application to unsuspecting pieces.  The existence of clay crumbs in work
> to be bisqued guarantees constant additions to the bucket bottom 
> collection.
> I am probably no less guilty of making those additions to the bucket than
> anyone else; my anguish at a sharp point on the shoulder of my otherwise
> perfect (aren’t they all) pot after firing is as great as anyone’s.
> If one has their own work space, frequent screening of the glaze slurry
> before use helps limit goobies. More care to remove clay crumbs from ware
> before bisquing will also help.
> I have sometimes wondered what role selective removal of lighter glaze
> components plays in inconsistent glaze results.  Not all users will
> throughly stir the glaze bucket before use or will use the bucket for a
> long time without a re-stir.  This practice must selectively remove slow
> settling glaze components from the mix at some unknown rate.  The
> succeeding batch of added glaze would be unintentional enriched in heavier
> components.  But does it make a difference?
> There are so many variables in our “sport” this one may not be important.
> Joe
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