[Clayart] Measuring Glaze Thickness

Tue Feb 18 00:17:06 UTC 2025

I use a photographer's darkroom cylinder to measure my glaze gravity.
The cylinder weighs 123 grams when empty.
I fill the cylinder to the 1000 ml mark, place it on my scale, record the weight in grams, and then subtract the weight of the empty cylinder. The resulting figure is then divided by 1000, simply by moving the decimal three places to the left. The result is the gravity of the glaze.
For example, with my transparent glaze: I fill the cylinder to the 1000 ml mark, and it weighs 1,563 grams. I then subtract the empty cylinder weight, leaving me with 1,440 grams. I divide this figure by 1000, moving the decimal three places to the left, which gives me a glaze gravity of 1.444. I round it to 1.44. I dip my pieces using a 3/1000 count.
When developing a new glaze, I set aside five small bisqued bowls and prepare the new mix to a gravity of 1.50. I take the first bowl, marked #1, and dip it into the glaze for a 3/1000 count. I then adjust the glaze to a gravity of 1.48 and repeat the 3/1000 count for the second bowl, marked #2. I continue adjusting the gravity—1.46 for bowl #3, 1.44 for bowl #4, and 1.42 for bowl #5—each time dipping for a 3/1000 count. After firing the bowls, I select the gravity that produces the most desirable result. If the glaze is too thick or too thin, I repeat the test using a 2/1000 or 4/1000 count.
This method can also be used to determine the ideal glaze gravity when double-dipping or layering one glaze over another.
If viscosity is adjusted, the dipping count time may need to be readjusted accordingly.
I hope this description is clear.
Best,
Terry—currently under 80 centimeters of snow.

________________________________
From: Clayart <clayart-bounces at lists.clayartforum.com> on behalf of kathi--- via Clayart <clayart at lists.clayartforum.com>
Sent: Monday, February 17, 2025 4:05 PM
To: Clayart international pottery discussion forum <clayart at lists.clayartforum.com>
Cc: kathi at lesueurclaywork.com <kathi at lesueurclaywork.com>
Subject: Re: [Clayart] Measuring Glaze Thickness

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=
>>
>>
>>
>> --
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