Note: This article is from Jesse Wiseman Hull’s website, now archived here.
Monday, January 28th, 2008
A glaze recipe is almost always listed as a “percentage or batch formula”, adding up to 100. Every once in a while you’ll run across something that is slightly off (I was shown one adding up to 98.63% recently) -but that’s uncommon.
As stated in my post “Getting Started with Crystalline Glazes“, when people ask me for a crystalline glaze recipe (^9-10), I offer them this to start with:
Frit 3110: 50 %
Zinc Oxide: 25 %
Silica: 25 %
50 + 25 + 25 = 100 %
The above would technically be referred to as a percentage formula . If you wanted to make a small test, you’d probably just want to mix up 100 grams.
This would then be called a 100 gram batch formula :
Frit 3110: 50 grams +
Zinc Oxide: 25 grams +
Silica: 25 grams
= 100 grams
Ok, so say you find that the glaze works, and you want to mix up 600 grams to test further…
Look at the above formula again, like this:
Frit 3110: 50 (x 1) = 50
Zinc Oxide: 25 (x 1) = 25
Silica: 25 (x 1) = 25
= 100 , right?
So for 600 grams:
Frit 3110: 50 (x 6) = 300 +
Zinc Oxide: 25 (x 6) = 150 +
Silica: 25 (x 6) = 150
= 600 grams
For 800 grams, multiply each part by 8 ,
for 950 grams, multiply each part by 9.5 ,
and for 1000 grams, multiply by 10 .
In John Britt’s book “Complete Guide to High Fire Glazes”, I list an Alkaline Base Recipe:
Frit 3110: 51
Calcined Zinc Oxide: 23
Silica: 22
Grolleg Kaolin: 2.5
Alumina Hydrate: 1.5
= 100 %
The above formula is called a base glaze . Base glazes typically come out clear or white. To this you can add colorants, modifiers, binders, etc. These are not usually listed as part of the formula, but you’d still multiply each one by the same number, to get an equal proportion in the glaze.
For 750 grams…
Frit 3110: 51 (x 7.5) = 382.5 grams
Calcined Zinc Oxide: 23 (x 7.5) = 172.5 grams
Silica: 22 (x 7.5) = 165 grams
Grolleg Kaolin: 2.5 (x 7.5) = 18.75 grams
Alumina Hydrate: 1.5 (x 7.5) = 11.25 grams
To get the dark blue glaze pictured on pg. 137 of Britt’s book, add:
Cobalt Oxide: 3 (x 7.5) = 22.5 grams
Manganese Dioxide: 3 (x 7.5) = 22.5 grams
Red Iron Oxide: 3 (x 7.5) = 22.5 grams
Bentonite (or CMC as a binder): 1 (x 7.5) = 7.5 grams
So you have 750 grams of the base + 75 grams of colorant and binder = 825 grams.
Now you can use that result to calculate how much water to add.
