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Understanding Ceramic Glazes

Glazing is perhaps the most difficult aspect of ceramics and the one for which you bear the most accountability (for design, functionality, and safety). It is important to know 'why' glazes do what they do. It is better to 'understand' and control a few glazes than struggle with many that end up controlling you. Watch out for the dragon who seems innocent at first. The traffic in glaze recipes and the trend toward abdicating control to suppliers and consultants, these mentalities breed ignorance and invite trouble. Formulate your own glazes.

To understand the complexities of glazes one must marshal several different viewpoints, that is, understand things on different levels. There is usually no one simple answer for formulating or fixing a glaze. We recommend you develop the ability to determine which level is most closely related to the problem at hand. Study the trouble shooting articles at the bottom on this page and note how thinking in terms of these four levels helps to formulate questions that lead to solutions.

The Process Level: The technician immerses himself in understanding the equipment used to apply, dry, decorate, fire, and cool the ware. By fine tuning these devices he exercises considerable control over standard plant or studio recipes or glazes purchased ready made from suppliers. When problems arise he/she analyses them mainly in terms of changes he can make to the process.
The Recipe Level: The technician test mixes many glaze recipes or commercially prepared glazes hoping to find one that 'appears' to be visually suitable. When problems are encountered, a recipe is often discarded and the pursuit of another begins. On this level little is learned when a recipe does not work properly. Leaching and crazing 'consciences' tend to be underdeveloped. People trapped in this culture tend to feel quite helpless, glazes are 'mysterious' to them. Many want to have guaranteed solutions handed to them yet they are very tolerant of touchy, difficult, and expensive recipes. Many believe the 'fool proof' recipe is just around the corner.
The Material Level: The technician learns what materials do when fired and uses trial and error blending to produce glazes. He is able to achieve a degree control over the fired visual character and gains confidence. Much more is learned when glazes do not fire as expected. The physical working properties of glazes can be rationalized according to the properties of the components and adjustments made to improve application or mixing properties while maintaining fired characteristics. This approach is particularly applicable to decorative and non-functional products where the pursuit of interesting surfaces is very important. However this method falls short when it comes to producing functional surfaces and exercising greater control of diverse fired properties. Material level formulation tends to perpetuate the acceptance of results based on visual appearance only. Flux saturated glazes are examples of the products of this approach, yet they are usually unstable against chemical or mechanical attack.
The Oxide Level: The technician understands the function of oxides, the building blocks of the final fired glass. He has much greater control of many fired properties that are related directly to specific oxides or oxide systems. When problems occur this level often teaches valuable lessons that can be applied to solve current and future problems. When both the material and oxide levels are considered the technician can achieve a measure of 'material independence' (he can choose what mix of materials is best to supply a given formula of oxides). While things like blistering and crawling can be understood best by considering both the material and oxide mix of a glaze, issues like crazing and color development can only be fully grasped without consideration at this level. Each oxide has well documented contributions and interactions with others in the fired glass and proper understanding of the oxide level provides strategies for dealing with all kinds of glaze properties (i.e. hardness, surface character, crystal development, chemical stability).

We encourage you to learn about materials and ceramic calculations.

The Magic of Fire book is available on line and it has many chapters to help you understand glazes.

Ravenscrag Slip - Plainsman Clays
A new silty low iron clay that applies evenly, drains dripfree, dries hard, doesn't settle. Melts to glossy clear at cone 10, add frit/feldspar for lower fire, silica for gloss. Use as base, add colorants, opacifiers, variegators. Use as an underlayer for vibrancy in fluid glazes without associated running. Use multilayers on green/bisque without crawling or cracking; opens a whole new area of decorative effects with colored and fluid/non-fluid multi-layers. Excellent for students to learn glaze formulation. Supported by internet community and website.
Ceramic Glazes Today - Todd Barson, Ferro Corporation
A brief outline of trends in various industry segments, trouble shooting and testing glazes by someone who really knows.
Ceramic Stains - Digitalfire Corp.
What are they and how to you use them properly?
How to Glaze-Liner a Mug - Digitalfire Corp.
Using a liner glaze is a way to protect your customers. But how do you apply the inner and outer glazes so that they meet in a clean line?
Testing Your Glazes Thoroughly - Digitalfire Corp.
What if you could greatly improve the quality of your glaze with some simple tests? Would you do them?
Do You Need to Know About Eutectics to Make a Good Glaze? - Clayart Contributors
Knowing about eutectics provides a kind of insight about glaze melts that you may not have expected.
Copper Red Glazes - Karl Platt
A detailed technical discussion about the mechanisms that produce the most successful copper red glazes.
Understanding Glaze Calculation: An Aid to Potters - Bob Kavanagh
A complete tutorial that summarizes the purpose of calculations, reviews the theory, and demonstrates with Hyperglaze and INSIGHT.
What is a Mole - Joseph Herbert/Tom Buck
You read this right. Understanding what a 'mole' is turns some lights on when it comes to understanding ceramic chemistry.
Are Your Glazes Food Safe? - Digitalfire Corp.
Responsible manufacture of pottery requires that you give attention to what is known about glaze leaching and what you can do about it.
Making Your Own Cone 6 Base Glaze - Digitalfire Corp.
An elegant and flexible cone 6 base glaze with information on how we formulated it. We use this recipe as a 'home base' and rationalize others in terms of it. For an optimized glossy base see the page on our G1214W recipe, for an adjustable velvety matte visit the page on our G1214Z recipe.
Making Your Own Cone 10/10R Glaze - Digitalfire Corp.
Starting recipes for cone 10/10R base glossy and matte glazes that you can understand and control and change to your needs.
Making Your Own Cone 06-02 Glaze - Digitalfire Corp.
Starting recipes you can understand and control..
Making Majolica Work - Digitalfire Corp.
A complete description of how to create and control your own transparent and white glazes at cone 04-06.
First You See It Then You Don't - Tom Buck
Raku glazes with their often spectacular lustrous effects continue to interest potters and public. But, as letters in Ceramic Review and other journals indicate, the lustres often lose their brilliance with time. Here, Tom Buck suggests strategies for adjusting glazes to enable them to retain their lustrous glow.
Super Refined Terra Sigillata - Vince Pitelka
Step-by-step instructions on how to make and apply terra sig to get a mirror finish on earthenware pottery.
Making a Glaze Slurry Work Well - Digitalfire Corp.
A consideration of techniques you can use to make your glaze apply evenly to any ware and never settle out in the container.
Calculating Crazing - David Hewitt/Mike Bailey
A detailed consideration of thermal expansion theory and how to calculate it.
Those Unlabelled Bags and Buckets - David Hewitt/Mike Bailey
How to identify unlabelled bags of materials.
Glaze Bubbles - Gavin Stairs
An interesting look that the causes of glaze bubbles.
Does Crazed Ware Present a Bacteria Hazard - Gavin Stairs
A well rounded look at what to consider if you are thinking about marketing crazed ware as functional ware.
Floating Blue Glaze Recipe Cone 6 - Jonathan Kaplan
He says it best: "to continue to butt heads with this glaze seems to me counter productive"
Volcanic Ash - Joseph Herbert
Everything you ever wanted to know on this subject.
Variegating Glazes - Tony Hansen
How to give flat 'porcelain-sink' glazes a lively variegated surface.

Trouble Shooting

One of our customers said it best: "There never seems to be just one reason for a problem!". The following pages recognize that your analysis must approach things on different levels and recognize the interconnectedness of the physical and chemical properties of glazes.

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Phone Phone: (406) 662-0136

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