[Clayart] an approach to expensive glaze materials
John Post via Clayart
I did a few things to evaluate the material cost of the glazes being made
there.
First, I entered all of the Art Center's glazes into Glazy.org.
I then went through our material invoices and calculated the cost of raw
materials by the pound, including shipping. (We order from U.S. Pigment.) I
entered these material costs into Glazy.
Using Glazy’s recipe batch page, I calculated the cost of each glaze per
bucket.
Almost every glaze we inherited contains either Gerstley Borate, Spodumene,
Lithium Carbonate, or Tin Oxide. Some of our glazes were in the $200 per
bucket range.
As I teach my students to use biaxial blends, triaxial blends, line blends,
and 50/50 colorant blends, we work with glaze bases that *do not contain
Lithium, Gerstley, or Tin.* Because the glazes students discover are
created *without* those materials, they are automatically much more
economical than the old glazes. (We're in the $30-50 a bucket range with
the new glazes.)
To use Boron, we’ve replaced the overly expensive—and increasingly
rare—Gerstley Borate with frits. Our studio now formulates glazes using
frits 3134, 3124, 3195, and 3110. The last bag of Gerstley the studio
purchased cost $350. Bags of frit from U.S. Pigment are in the $150 range.
In the glaze course, I have students find their own glaze recipes on Glazy
to use as a base for exploration in a biaxial grid. The result of the 5x5
biaxial grids students create is 25 glazes that share the same fluxes but
vary in amounts of alumina and silica. This yields a wide variety of
surfaces, with students discovering new glaze surfaces they like.
We have cone 6 liner white, a clear, a celadon, an iron red and some chrome
tin pinks that came out of this approach as well as a wide variety of Earth
tone glazes. With the biaxial grid glazes interacting with the clay bodies
we use in the studio it is impossible to predict where the sweet spot for
interesting glazes will be on any grid. But there usually is one or more
and then the students explore those glazes in more depth.
Our solution to the Lithium and Gerstley price hikes and rarity is to just
make glazes without those materials. None of the students in the glaze
class is upset that we are no longer going to buy those materials because
they have experience getting glazes they like with frits as the boron
source at cone 6.
That's our approach to the price increase. We're taking it as an
opportunity to find and make new glazes for our studio as opposed to a
challenge to source lithium with either sodium or potassium.
Cheers,
John Post
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Terry Lazaroff via Clayart
I used a similar approach when I calculated the cost of producing my mugs, specifically the glaze cost. Here’s the process I followed:
1.
Weighing the bucket – I first recorded the weight of the empty bucket.
2.
Mixing the glaze – I prepared a 10,000-gram batch of glaze and weighed the bucket again once it was full.
3.
Finding the glaze weight – By subtracting the empty bucket’s weight, I obtained the net weight of the glaze mixture (all measured in grams).
4.
Checking consistency – I measured the specific gravity of the glaze to ensure the mixture stayed consistent for future use.
5.
Cost per gram – Using the total cost of the ingredients and the glaze’s net weight, I calculated the cost per gram of the glaze.
6.
Glazing the mugs – I then glazed 20 mugs.
7.
Re-weighing – After glazing, I weighed the bucket again and subtracted the empty bucket’s weight to find the remaining glaze.
8.
Glaze consumed – The difference between the original glaze weight and the post-glazing weight gave me the total glaze used on the 20 mugs.
9.
Average per mug – Dividing that amount by 20 provided the average glaze used per mug (in grams).
10.
Cost per mug – Finally, multiplying this average glaze weight by the cost per gram gave me the glaze cost per mug.
To maintain accuracy, I always checked that the glaze’s specific gravity stayed constant whenever I reused glaze from the same bucket. This ensured the cost per gram remained valid.
While some might see this as over-detailed, it only needs to be done once—provided the glaze mixture remains consistent. After that, the cost per mug becomes a fixed input in overall production costs. For hobby potters this may feel excessive, but for anyone producing larger batches, it provides a reliable way to calculate one important cost variable across mugs, bowls, plates, or any other items.
Terry
Closed 1001Pots today. It was a great show. Today's action was what I call, frenzy feeding. Holidays were coming to, an end and people were going home. This was the last time for them to grab some great pots.
________________________________
From: Clayart <clayart...@lists.clayartforum.com> on behalf of John Post via Clayart <cla...@lists.clayartforum.com>
Sent: Sunday, August 17, 2025 12:21 AM
To: cla...@lists.clayartforum.com <cla...@lists.clayartforum.com>
Cc: John Post <johnp...@gmail.com>
Subject: [Clayart] an approach to expensive glaze materials
robert hackert via Clayart
Rob Hackert
Sent from my iPhone
> On Aug 17, 2025, at 5:55 AM, John Post via Clayart <cla...@lists.clayartforum.com> wrote:
>
> In retirement, I teach a glaze-making class at the Sedona Arts Center.
John Post via Clayart
*Jen's Juicy Fruit Base*
EPK 10
Gerstley Borate 9
Lithium Carbonate 9
Whiting 11
Neph Sy 49
Silica 12
additions
Soda Ash 10
Titanium Dioxide 5
I used 3 % black iron in two different variations
One had 1.5 % Black Nickel in it
The other omitted the Nickel and replaced it with .75% Cobalt Carb
Jen's Juicy Fruit is not my recipe. I may have gotten it from the Ann Arbor
Potters Guild Website in the early 2000's.
People attribute it to me because I posted a bunch of photos of test tiles
I made with colorant variations on my website back then.
Best,
John
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