[Clayart] Measuring Glaze Thickness

Mon Feb 17 21:05:14 UTC 2025

This is how I do it. I have a beaker that will hold 100 ml. I pour the glaze in and weigh it. Easy
Sent from my iPad

> On Feb 17, 2025, at 3:37 PM, Paul Randall via Clayart <clayart at lists.clayartforum.com> wrote:
> 
> Whatever. My current syringe only holds 60cc. Each potter is different, each potter has their own working state.
> Paul
> 
> Get Outlook for iOS<https://aka.ms/o0ukef>
> ________________________________
> From: Clayart <clayart-bounces at lists.clayartforum.com> on behalf of Dragonbelly Ceramics via Clayart <clayart at lists.clayartforum.com>
> Sent: Monday, February 17, 2025 11:27:19 AM
> To: Clayart international pottery discussion forum <clayart at lists.clayartforum.com>
> Cc: Dragonbelly Ceramics <lisa at dragonbellyceramics.com>
> Subject: Re: [Clayart] Measuring Glaze Thickness
> 
> Isn't is simpler to weigh the empty syringe and tare it, then weigh the
> glaze-filled 100 ml syringe, and simply move the decimal point 2 points to
> the left?
> 
> 100 ml of water weighs 100 grams.
> 
> If your 100 ml of glaze weighs 140 grams, the specific gravity is 1.4
> 
> Am I missing something?
> 
> LJ
> 
>> On Mon, Feb 17, 2025 at 1:07 AM Robert Santerre via Clayart <
>> clayart at lists.clayartforum.com> wrote:
>> 
>> Yeah Dick, this same method of measuring specific gravity of a glaze can
>> be done quite precisely with a 100 ml graduated cylinder (glass or plastic)
>> that can be readily purchased online.  And if the cylinder gets broken, it
>> can be readily and cheaply replaced.  Weigh the empty cylinder, then fill
>> it with water to the 100 ml mark and weigh the filled cylinder.  Then pour
>> out the water, fill the cylinder to the 100 ml mark with your glaze mix,
>> weigh it and make the calculation ... weight of the glaze mix minus the
>> weight of the empty cylinder divided by the weight of the water minus the
>> weight of the empty cylinder = specific gravity of the glaze mix.  Quick
>> and easy, very repeatable and quite precise/accurate.
>> 
>> But, to be clear, specific gravity does not describe the "thickness" of a
>> glaze mix.  Thickness or viscosity describes the rheological property of a
>> glaze. It describes how the glaze flows, a mechanical property of the
>> glaze.  The “thickness”, flow or mechanical property of a glaze can be
>> influenced in many ways (independent of its specific gravity).  For
>> example, a glaze with a good amount of clay in it can be thickened by
>> adding small amounts of acid, like hydrochloric acid … or the thickness
>> (viscosity) can be decreased by adding small amounts of a base, like sodium
>> hydroxide. You can get a reasonably accurate measure of glaze “thickness”
>> by pouring a measured amount of a glaze into a funnel and timing how long
>> it takes for the glaze to pour out of the funnel.  The longer it takes to
>> empty out of the funnel the thicker, more viscose the glaze.
>> 
>> 
>> 
>> The two measurements (specific gravity and “thickness”) work together to
>> determine how much glaze you will apply to a pot.  In my experience glaze
>> viscosity is often the most important factor determining how much glaze you
>> are applying to a pot.  There are of course a number of other factors
>> influencing the amount of glaze applied to a pot, e.g., how long the pot is
>> held in the glaze, is the pot dipped in the glaze or is the glaze poured
>> over the pot, variations in the thickness of the bisqued pot (for example
>> the thickness the handle of a mug versus the wall thickness, etc., etc.
>> Lots of variables, many of which can only be determined and controlled by
>> the experience of the individual potter.
>> 
>> 
>> 
>> Again, in my experience that’s why glaze formulas don’t always travel
>> well.  The experience of the potter and his/her kiln are THE MAJOR
>> FACTORS.
>> 
>> 
>> 
>> Bob Santerre
>> 
>> formerly Arrowsic Island Pottery
>> 
>> //////////////////////////////////////////////////////////////
>> 
>> 
>> 
>> -----Original Message-----
>> From: Clayart [mailto:clayart-bounces at lists.clayartforum.com] On Behalf
>> Of Dick Lumaghi via Clayart
>> Sent: Sunday, February 16, 2025 5:58 PM
>> To: Clayart international pottery discussion forum
>> Cc: Dick Lumaghi
>> Subject: [Clayart] Measuring Glaze Thickness
>> 
>> 
>> 
>> 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=
>> 
>> 
>> 
>> --
>> This email has been checked for viruses by Norton antivirus software.
>> www.norton.com<http://www.norton.com>
>> -------------- next part --------------
>> An HTML attachment was scrubbed...
>> URL: <
>> https://lists.clayartforum.com/pipermail/clayart/attachments/20250217/cfeded49/attachment.htm
>>> 
>> 
> 
> 
> --
>        http://www.dragonbellyceramics.com
> *           where imagination meets function*
> -------------- next part --------------
> An HTML attachment was scrubbed...
> URL: <https://lists.clayartforum.com/pipermail/clayart/attachments/20250217/80cc1e80/attachment.htm>
> -------------- next part --------------
> An HTML attachment was scrubbed...
> URL: <https://lists.clayartforum.com/pipermail/clayart/attachments/20250217/c4dd7e35/attachment.htm>