December 8, 2006, Newsletter Issue #219: Understanding %īs

Tip of the Week

Glaze recipes are typically expressed by listing each raw material and its % by weight. The percentages add up to 100 Usually colorants and sometimes other additives (such as bentonite for suspension) are not included in the 100%, they are added on afterward.
Example:
Cone 6 Clear Base Glaze

Wallastonite 10%
FRIT 3134 30%
Kaolin 25%
Flint 15%
F-4 Feldspar 20%
Total 100%
Add 4% cobalt oxide for a deep blue
To mix this glaze, you take the total number of grams of dry material you are making, multiply by the % to get the grams of each material to add.
Example:
To make 1000g of glaze
Wallastonite = 10/100*1000=100 grams
FRIT 3134=30/100*1000=300 grams
Kaolin = 25/100*1000=250 grams
Flint = 15/100*1000 = 150 grams
F-4 Feldspar = 20/100*1000 = 200 grams
To double check, add up all the grams and make sure they equal 1000.
Then add 4/100*1000 = 40 grams cobalt oxide
This is as far as many people go. They make the glaze, test it, and often are unhappy with the results. We need to understand why!

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