As a glaze nerd I like to make rows. That’s why I use the “viewpoints” of Tony Hanssen (digitalfire) when analyzing glazes. From him I learned four glaze levels:
- Process
- Recipe
- Material
- Oxide
In developing a glaze I have always had this theoretical framework in mind. I greatly benefit from this to achieve desired results, a finish that fits my ceramics.
In recent years more and more public data are available, also in the field of glazes. Can these new insights be incorporated into the existing framework or is it time for more perspectives?
Four glaze levels for analysis
If you’re designing something, you should first look at what you want or rather what problem the design needs to solve. This is no different for designing a glaze. What do I want? A ceramic finish that “fits” with the ceramics that I make.
A surface design is part of the total design. This total design also determines which surface treatment is desired. But for this part we only look at the glaze (after all we assume that’s what we want as a finish). So if we know what we want (a nice, reliable and strong glaze) then we can get to work.
But where to start? At the four glaze levels!
The process, the recipe, the material and finally the oxides. But not necessarily in this order. Sometimes the process is the starting point, for example when firing with wood. The process will (partly) determine the glaze and results.
Sometimes the material is the starting point, for example a wood-ash glaze. Alternatively, we can also look for a “look a like” glaze (a “fake ash glaze”). The starting point is then the oxide mechanism that can imitate a wood-ash-like glaze. So then we look at the oxide level.
But first let’s look at the glaze levels separately.
1. The process level
The process level is about making, applying and firing glazes. A glazing process has a lot of influence on the end result. Salt firing by definition results in a salt glaze. A wood firing gives a different result (with the same glaze recipe) than firing in an electric kiln.
The application method of the glaze, such as spraying, pouring or dipping, will also give different results. And then I assume that everything goes as planned at this stage of the ceramics battle.
At this level, things can go wrong too. A weighing error when making. Too thinly applied glaze. A wrong firing temperature, too little reduction (or too much) when firing. There are endless process failures. And if this doesn’t go well, no glaze recipe can save the ceramics….
2. The recipe level
A glaze recipe is just like a recipe for a cake. There are ingredients (flour, eggs, sugar) and there is a quantity. Sometimes exact (150 grams flour), sometimes globally (a pinch of salt). A glaze recipe is usually written exactly in percent weight, but sometimes also in volume (a pinch). I love exact (and carrot cake), but tastes differ…
This is the level where a lot of ceramists start to make a glaze. A recipe of an acquaintance, from a book or from the Internet can be the beginning of an exciting glaze adventure.
This is also the perspective where the glaze analysis begins. If I want to design a glaze, this is where I start looking. Is there a recipe known, are there similar recipes and what are the experiences from potters who used them.
3. The material level
As mentioned, a glaze recipe is a list, just like a cake, with “ingredients”. In a glaze you usually speak of materials or raw materials. In a cake recipes sometimes exotic herbs (cardamom) are added, with glazes it is also like that, but there are so many that you soon lose count.
There are literally hundreds of glaze materials. In the glazy.org database there are now about 1,500 registered, but there are many more. Some are commonly available (e.g. quartz and kaolin), some are difficult to obtain or no longer for sale.
How do you know all (available) materials? By looking! A good place to start is a supplier of ceramic materials. And if you are there, ask for the datasheets of these raw materials.
The datasheet lists, among other things, all the different molecules of that material. These molecules always consist of one or more oxygen (oxide) atoms bound to one or more other atoms from the periodic table. Because these raw materials are always bound with oxygen, ceramists usually speak about “oxides”.
There are hundreds of materials, but these all consist of a handful of these “oxides” (in chemistry formulated as “O”). As for example quartz (SiO2), aluminum (Al2O3) and sodium (Na2O). In the datasheets all these oxides are, like a glaze recipe, neatly presented with a weight percentage.
For an example you can look at the materials section of glazy.org
4. The oxide level
Now we have arrived through the materials at the last level, that of the molecules and atoms. As mentioned above, ceramists usually call this “oxides”. If we do not count the coloring oxides, there are about 12. From hundreds of different materials to just over 10 different oxides, that’s a huge simplification!
There are many books written about the glazing process, the (role of) materials and glaze recipes (the first three levels). Without this knowledge and control of the process no ceramist can make it. With it, ceramists have designed the most beautiful glazes for thousands of years. The best examples come from the East like celadon, copper red and shino glazes.
But that does not mean that we should skip the oxide level. For decades now, software has been developed to make it easy to analyze at this level. Desktop software such as Insight by Tony Hanssen, Matrix by Lawrence Ewing or Hyperglaze by Richard Burkett.
Nowadays there are also websites where these calculations can be made online, Glazy.org is by far my favorite.
Trends and Forecasts
Analyzing glazes on these four glaze levels is nothing new. At the end of the nineteenth century, Hermann Seger demonstrated that the oxide level offers many advantages. The Seger Formula or U.M.F. (Unity Molecular formula) developed by him is still the best way.
In the twentieth century, a great deal of research has been done in this area. One of the first who continued the work of Seger was R.T. Stull and more recently Matt Katz. Using a more extensive version of the U.M.F. and the Stull chart, trends can be discovered and explained.
Using the recipes database on Glazy.org, glazes can not only be analyzed, but also forecasts are made about the appearance and melting temperature. Trends of specific glazes are becoming more and more visible, the more (reliable) data becomes available.
With Glazy a huge step has been made into the future of glaze analysis based on (big) data. I can’t wait how this evolves…
More reading
A lot of information can be found on the Glazy help page . If you prefer to read a book, you can look at my book page for more information. Unfortunately some books are no longer in print.
What about new books? Recently, a Book of Gabriel Kline has been published “Amazing glaze, Techniques, Recipes, Finishing, and Firing“. This is an excellent introduction to glazes. Unfortunately he also skips the oxide level, but process, materials and recipes (the three other glaze levels) he describes very well.
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