[Clayart] Measuring Glaze Thickness

Mon Feb 17 17:27:19 UTC 2025

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
> -------------- 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>