Changing an Ingredient in Glaze Recipes
- , by Haley Stanaford
- 3 min reading time
Raw materials have been coming and going a lot. We’ve had to say goodbye to some amazing materials like Custer Feldspar and talc. So what do you do when you have to say goodbye to these materials? Do you just throw out the glaze you love? No! Reformulate it.
Let’s take Tony Hansen’s G1216M - Cone 6 Ultraclear Glaze for Porcelains for example. This glaze has minspar 200, frit 3134, wollastonite, epk, talc, and silica. We no longer have talc. So let’s reformulate it.
We’re going to put this recipe into Glazy’s UMF calculator. UMF, the unified molecular formula, is how we can analyze the makeup of glazes and to change them if needed.
What I am currently concerned with are the numbers under the materials. These numbers are explaining the glaze’s composition and how it will look after firing. I want these numbers to stay exactly the same when putting in a different material.
The R2O:RO is Alkali to Alkaline Earth metals while the SiO2:Al2O3 is the Silica to Alumina Ratio. The Alkali metal to Alkaline earth metals ratio is controlled by the compounds present. The calculator actually tells us by color coding the Alkali and Alkaline earth metal compounds! The alkali metals are in red (the Na2O and K2O) while the alkaline earth metals are the blue (CaO). These compounds come from the raw materials we add to the glaze so we are going to try our best to keep these numbers as close to the same as possible.
Using this calculator I can also see where these compounds are coming from by clicking the drop down menu under the graph and clicking percent.
In this analysis, I see talc is providing 2.73 SiO2 (Silica) and 1.37 MgO. So now that I know what it is bringing to this glaze, I know to replace those components. The easiest way to do this is to find a similar material and then adjusting the numbers to match the original ones.
I can head on over to our best friend, digital fire again and see every material and the chemical analysis for them and I can find one that is similar to talc.
The closest I can get to talc is Magnesite, or magnesium carbonate, which will supply the MgO. Now for the SiO2, I know from my percentage chart of the UMF on Glazy, that the silica in the recipe is mostly coming from the Silica/Flint, so I can raise that number higher. After taking out the old material and putting in a new one, it becomes a guess and check game. I need to compare the old numbers (which I like to have to the left of my screen for quick comparisons) with the new ones and play with the silica and Magnesium carbonate numbers until they are close to the original.
Yay! I did my guess and check game, paying attention to every movement of the numbers and how they controlled the analysis and got the same numbers!! Yippee!
Now, my batch total is 101.10%. So I can click the 100% button right above “New Analysis” and it will set my batch to 100% for me! Thanks Glazy!
So there you have it. With some raw materials going away and others becoming so expensive, you are able to change your recipes. All is not lost! However, this is not to say that this is a perfect fix. Problems can and will be encountered by changing some materials for others as materials have different personalities and will behave differently in the presence of others. It is always important that you test your glazes (make sure to use a cookie). The UMF calculator is great and a very useful tool, but make sure the recipe works in practice!
Haley Stanaford is currently a Post Baccalaureate student in ceramics at the University of Kansas where she is currently taking a Clay and Glaze Formulation taught by Colby Charpentier in addition to her studio practice. She also is a Sales Representative at Bracker’
