[Clayart] Measuring Glaze Thickness

[Dick Lumaghi]

The recent mentions on Clayart of the Shaner’s Red glaze prompt me to respond.  That glaze, along with one or 
two varieties of a Cushing Mat glaze, gave me fits when I tried to measure its thickness accurately.  I tried various
hydrometer methods—the cheap and dirty use of a stick with a bolt screwed into one end with gradations along
the stick, or a battery tester with the bulb—and they just didn’t work for me. I happened to bump into a potter who
did the weighing method and it was transformative for me.  Yes, it took a bit of time to check all the buckets of 
glazes at the beginning of “Glaze Day”, but the results were, for me, wonderful: FINALLY some certainty about
these most finicky glazes, and now I use it with all my glazes. Here’s my method:

I got lucky and found a generously sized, double walled plastic coffee cup with a good handle.  It holds about 500 
grams of glaze and that seems about right to get consistent results.  Most importantly, the cup happened to have a 
rather sharp top lip, where the two walls were joined together. So what I do is place my triple beam scale on a box 
resting on the sink table so that when the cup is on the scale, its top is eye level.  I stir up the glaze with a Jiffy mixer
and a drill, pour a good amount into the cup, place the cup on the scale, and finish adding glaze with a turkey 
baster until there is a nice meniscus (the bulge from the liquid’s surface tension trying to hold the liquid inside
the container) and then I read the weight and note it down. That sharp edge of my cup seems crucial to holding
exactly the same amount time after time.  When I get a weight that works, I put it on the glaze notes I have on the 
wall and on the bucket as well.

Perhaps this is no news to most of you and I cannot claim any originality with this method.  I did, however, have 
a (rare) flash of inspiration that may be novel.  It occurred to me that if I somehow lost or broke my precious cup, I’d be 
sunk—all that work having to be done again.  I was a pretty rotten math student, but something must have remained,
for I got the idea to weigh the cup full of water and note that weight in my records so that I could have a factor to measure
against any other container in the future. 

I’ve been doing this method for over 40 years and it occurs to me that perhaps there are more up to date ways to do this
and I’d be open to hearing about them.

Thanks.

Dick Lumaghi
dlumaghi at cybermesa.com