•The secret to cool bodies and glazes is a lot of testing.
•The secret to know what to test is material and chemistry knowledge.
•The secret to learning from testing is documentation.
•The place to test, do the chemistry and document is an account at https://insight-live.com
•The place to get the knowledge is https://digitalfire.com
Where Do I Start?
Section: Glazes, Subsection: Introduction
The perfect universal glaze recipe does not exist, the only way you will get the glazes you really need is formulate or adapt them yourself. Start with base recipes, learn to understand them from a material level, then learn the mechanisms, and chemistry.
Probably you are reading this because you are starting to mix your own ceramic glazes and are overwhelmed. Or you have done something a certain way for years and now it is not working. Or your company expects you to fix problems for which you do not have the training.
There is a prevailing culture in pottery, hobby ceramics and even industry of getting by with the least knowlege possible. Somehow we want to believe that we can mix a recipe we find on Pinterest.com and it will magically work just like the picture. You may have realized by now that this site is dedicated to fighting that culture (which we personify as "the glaze dragon"). We recommend that you embark upon a journey of understanding as follows:
- Find good glossy, matte and fluid glossy base recipes in your temperature range. Work with these and adjust them to fit your clay. Substitute your materials and fix other issues (e.g. poor suspension or application properties, excessive drying shrinkage). Then add colorants, opacifiers and variegators to these. Be slow to bring a new recipe into your operation unless you understand it. Could you add its colorants, opacifiers and variegators to a base recipe you already have? If you are in cone 6, for example, click the Recipes link above and go to the recipes G2934, G2926B and G3806C.
- Learn more about the materials you are using. Are they there to make the glaze melt? To color it? To suspend it in the bucket? To variegate the color or opacify the glass? To make it crystallize on firing? To matte it? Etc.
- Learn about how to make a slurry suspend well in the bucket and apply well to the ware.
- Practice spotting the 'mechanisms' in recipes. What is the material or chemical reason for why they fire the way they do? When you see recipes mentally disassemble them into thier base recipes and additions.
- Although you are not a chemist you likely realize that fired glaze properties like gloss, color, thermal expansion, hardness, melting temperature, etc are most directly related to the chemistry of the glaze. What exactly do we mean by "glaze chemistry"? It means simply that you view your glazes as made of oxides like SiO2, Al2O3, Na2O, etc and your materials as suppliers of them. The oxide makeup of a glaze is called a "formula". There are about 10 oxides to learn about, all of your raw materials are composed of them. Recipe management software automatically displays the chemistry.
- Learn to be demanding. Do no accept naked, undocumented recipes. Do not accept problems like crazing, scratching, leaching, settling in the bucket. Learn to fix them. Don't work with temperamental glazes (e.g. rutile blues) unless you understand them well. Do not accept high reject rates.
- Do not waste time, be willing to work. Do lots of testing. Most of your tests should be smaller changes to recipes you have so you can learn something. Do not be afraid of failure, it teaches us.
- Document. Document your failures. With good pictures. Use an account at https://insight-live.com to record every recipe you make, every test firing, every project. You will find the ability to see recipes side-by-side with pictures and chemistry invaluable in determining what changes to make next. Your account will also immerse you in reference material so you will be learning constantly.
- Watch my timeline at https://digitalfire.com and at Facebook and Twitter (links below).
Are you at a school, art center or club?
- Does your school have a few recipes that are treated as if they were "dropped from heaven"? There is plenty of information on this website to help you improve them. Learn how to determine if you need to approach the problem on the material, process or chemistry levels.
- If you teach a class first learn to teach your students to understand materials and the physical properties they bring to the glaze slurry. Then introduce the concept of chemistry, how the materials source it to the glaze recipe and how it is the most important a determinant of fired glaze properties.
- There is a good chance that every single bucket of glaze is improperly mixed (has too little water). Read the article on Thixotropy (link below). If you can turn those rock-hard-on-the-bottom buckets into the most silky and easy-to-use glaze they have ever seen you will be a hero!
Are you at a factory?
- If consultants or supplier reps visit your company and mess about with your glazes but never stay long enough to explain anything or to really understand your issues then learn the chemistry and physics yourself.
- Wait for a crisis having a chemistry-related solution that is being mismanaged by narrow material-level thinking. Click the Trouble Shooting link above for more information.
- Does your company or organization have far too many different glaze recipes and stock too many materials? Learn to view materials as oxide suppliers. Study what each oxide does (click the Oxide link above). Review the lessons here on how to substitute different materials yet supply the same oxides. Read about base glazes and how to identify mechanisms so you can adopt a base-with-variations approach. In the end you will have fewer recipes.
- If you use commercial glazes and either cannot justify the expense anymore or cannot solve problems for lack of content information, then learn about base glazes and develop or adjust one to fit your body. Then experiment with stain and opacifier additions and study chemistry issues surrounding colors that do not develop as expected.
Places to start
- The best place to learn is to begin working through the lessons at https://digitalfire.com/videos. These teach all sorts of problem solving, formulation and adjustment techniques.
- The best place for on-line reference information is right here: use the articles, oxides, materials and glossary links above.
- If you are new to the concept of glaze chemistry we encourage you to start with an article on one of our base glaze recipes and learn why each material is there. Then learn to appreciate the value of having a base glaze that is adjustable, has the right gloss and melting temperature, has good application properties, fits your clay body, etc.
- Get and account at
https://insight-live.com and start entering the recipes you know and use already. Learn how to make it show the chemistry and compare them side-by-side.
If you are going to make ceramic ware, put good glazes on it. Remember, a glaze is a lot more than one that just has a pleasing fired appearance. There is no one-glaze-that-works-for-everyone. We cater to people that want to start out right, or have been kicked around long enough that they are ready to learn why, they want to "understand". You will never likely get the glazes you really want until you formulate or adapt them yourself.
The traffic in glaze recipe will burn your success!
A good matte glaze. A bad matte glaze.
A melt fluidity comparison between two cone 6 matte glazes. G2934 is an MgO saturated boron fluxed glaze that melts to the right degree, forms a good glass, has a low thermal expansion, resists leaching and does not cutlery mark. G2000 is a much-trafficked cone 6 recipe, it is fluxed by zinc to produce a surface mesh of micro-crystals that not only mattes but also opacifies the glaze. But it forms a poor glass, runs too much, cutlery marks badly, stains easily, crazes and is likely not food safe! The G2934 recipe is google-searchable and a good demonstration of how the high-MgO matte mechanism (from talc) creates a silky surface at cone 6 oxidation the same as it does at cone 10 reduction (from dolomite). However it does need a tin or zircon addition to be white.
Do you know the purpose of these common Ferro frits?
I used a binder to form 10 gram balls and fired them at cone 08 (1700F). Frits melt really well, they do not gas and they have chemistries we cannot get from raw materials (similar ones to these are sold by other manufacturers). These contain boron (B2O3), it is magic, a low expansion super-melter. Frit 3124 (glossy) and 3195 (silky matte) are balanced-chemistry bases (just add 10-15% kaolin for a cone 04 glaze, or more silica+kaolin to go higher). Consider Frit 3110 a man-made low-Al2O3 super feldspar. Its high-sodium makes it high thermal expansion. It works in bodies and is great to incorporate into glazes that shiver. The high-MgO Frit 3249 has a very-low expansion, it is great for crazing glazes. Frit 3134 is similar to 3124 but without Al2O3. Use it where the glaze does not need more Al2O3 (e.g. it already has enough clay). It is no accident that these are used by potters in North America, they complement each other well. The Gerstley Borate is a natural source of boron (with issues frits do not have).
Do your functional glazes do this? Fix them. Now.
These cone 6 porcelain mugs have glossy liner glazes and matte outers: VC71 (left) crazes, G2934 does not (it is highlighted using a felt marker and solvent). Crazing, while appropriate on non-functional ware, is unsanitary and severely weakens the ware (up to 300%). If your ware develops this your customers will bring it back for replacement. What will you do? The thermal expansion of VC71 is alot higher. It is a product of the chemistry (in this case, high sodium and low alumina). No change in firing will fix this, the body and glaze are not expansion compatible. Period. The fix: Change bodies and start all over. Use another glaze. Or, adjust this recipe to reduce its thermal expansion.
In pursuit of a reactive cone 6 base that I can live with
These melt-flow and ball-melt tests compare 6 unconventionally fluxed glazes with a traditional cone 6 moderately boron fluxed (+soda/calcia/magnesia) base (far left Plainsman G2926B). The objective is to achieve higher melt fluidity for a more brilliant surface and for more reactive response with colorant and variegator additions (with awareness of downsides of this). Classified by most active fluxes they are:
G3814 - Moderate zinc, no boron
G2938 - High-soda+lithia+strontium
G3808 - High boron+soda (Gerstley Borate based)
G3808A - 3808 chemistry sourced from frits
G3813 - Boron+zinc+lithia
G3806B - Soda+zinc+strontium+boron (mixed oxide effect)
This series of tests was done to choose a recipe, that while more fluid, will have a minimum of the problems associated with such (e.g. crazing, blistering, excessive running, susceptibility to leaching). As a final step the recipe will be adjusted as needed. We eventually chose G3806B and further modified it to reduce the thermal expansion.
Out Bound Links
G1214M Cone 5-7 20x5 Glossy Base Glaze
This is a base transparent glaze recipe developed for cone 6. It is known as the 20x5 or 20 by 5 rec...
G2926B - Cone 6 Whiteware/Porcelain Transparent Base Glaze
A base transparent glaze recipe created by Tony Hansen for Plainsman Clays, it fires high gloss and ultra clear with low melt mobility.
2014-02-06 - This is an adjustment to an original recipe named ...
G1916M Cone 06-04 Base Glaze
This is a frit based boron base glaze that is easily adjustable in thermal expansion, a good base fo...
Concentrate on One Good Glaze
It is better to understand and have control of one good base glaze than be at the mercy of dozens of...
Knowing about thixotropy will enable you to mix a ...
Tutorial Videos at Digitalfire
Target Formula, Limit Formula
The term 'limit formula' historically has typicall...
An oxide is a combination of oxygen and another el...
Decomposition is the breaking of inter-molecule bo...
G2934 - Cone 6 Dolomite Matte Base Glaze
A base MgO matte glaze recipe fires to a hard utilitarian surface and has very good working properties. Blend in the glossy if it is too matte.
2014-03-26 - This glaze is the product of a series of tests to ...
In Bound Links
Ceramic Oxides Overview
Ceramic formulation and adjustment technology can ...
Glaze and Clay Body Recipes
Recipes here are for demo purposes. Read th...
Glaze chemistry is learning what each oxide does i...
We have included this page to warn you about recip...
Identifying a mechanism means you identify the rea...
By Tony Hansen
Copyright 2003, 2008, 2015 https://digitalfire.com, All Rights Reserved