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•The secret to know what to test is material and chemistry knowledge.
•The secret to learning from testing is documentation.
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Brushing Glazes


In North America, the hobby pottery community has transformed in recent years toward the use of commercially prepared, gummed, paint-on glazes. Almost all potters in the past made their own glazes but now many have embraced the use of small bottles of paint-on glazes for some or all of their ware. Web sites selling pottery equipment and supplies (and physical stores) often feature glazes very prominently (a reflection of how popular and lucrative these are). You can make your own brushing glazes (see below).

Their advantages include:

-A wide range of colors and visual effects.
-Good in classroom settings. Labels are clear.
-Ability to layer.
-Avoidance of the need to mix or maintain larger buckets of dipping glaze.
-The ability to control thickness.
-The avoidance of runny, experimental or miss-mixed test glazes that ruin kiln shelves.
-The ability to glaze unbisqued ware (greenware), re-qlaze or glaze vitrified bisque.
-Food-safe, durable.
-Special effects very difficult to achieve on your own (e.g. metallics, reactives, bright colors, layered effects).
-Suppliers also love bottled, paint-on glazes. They make more money and inventorying, customer service and labour are reduced.

These paint-on glazes were always the mainstay of low fire hobby ceramics. They were often leaded or high-boron and painted on unfired green ware. It was practical because almost everyone used the same clay body (50:50 talc:ball clay), glaze manufacturers knew what to match their products to. But now paint-on glazes are main-stream at all stoneware temperatures. Commonly-known recipes and effects have been commercialized by every manufacturer. Many commercial glaze lines are typically a transparent base with different stains, variegators and opacifiers added (some manufacturers even specify the base and encourage users to make even more variations by adding their own stains).

Their disadvantages include:

-Expensive (double or more than you would pay if you mix your own). A potter going to resupply can spend thousands of dollars (as opposed to the hundreds he would spend for buying the materials to mix his own).
-Since the body and glaze manufacturers are separate companies, compatibility and fit between the products is purely by accident (thus crazing, shivering, going milky are much more common).
-The recipes are unknown. They claim they are food safe; but very bright colors, high melt fluidity, heavy crystallization; these are all often associated with leaching. And commercial glazes do all of these.
-They breed an ignorance of how glazes work. The recipes and techniques for a wide range of visual effects were once known by potters, and many knew how to tweek them for their circumstances.
-They breed an ignorance of how to maintain the specific gravity, viscosity and thixotropy of a slurry.
-They breed a weekend-warrior (as opposed to cottage industry) mentality in ceramics.
-When simple, clean, functional surfaces are needed (transparent or colored) it is very difficult to apply paint-on glazes in a professional, even manner. Dipping is the only way to apply totally evenly. Dipping versions of common bottled glazes are available, but they are commonly gummed also and dry and drip much more than non-gummed ones that potters can make.
-Paint-on is slow. Three coats with drying in-between can make glazing time much much longer than dipping.
-They often do not fire as expected (even though the supplier might have glossy and elaborate documentation).
-Stocks run out more frequently, often at very inconvenient times.
-Old dried-out or water-reduced jars are difficult to restore to working condition and it is impossible to sieve them.

Learn all you can about glazes and have all the advantages and none of the disadvantages!

Make Your Own

You cannot convert a dipping glaze into a brushing glaze by simply adding gum (in spite of what other pages might say). You cannot add the powdered gum because it will not mix into the glaze slurry. You cannot add gum solution because to get the 1-1.5% gum powder proportion needed at least 20% of the liquid content must be gum solution (meaning 20%+ of the water needs to be removed first. So it is better to start from scratch. Click the item in the links section below for a spreadsheet calculator. Fill in the numbers for your size jar and it will tell you how much glaze powder, water, gum solution to use.

How to convert a dipping glaze to a brushing glaze

How to convert a dipping glaze to a brushing glaze

I have a jar of testing clear glaze that I mixed myself (10% yellow stain and 2% zircopax added to cone 03 G2931K clear). Commercial glaze producers make their lines of glazes like this. The cost of the dry materials: About $6. How can I convert it to a paintable glaze like the commercial ones? I made a spreadsheet where I can specify the weight of the plastic jar, the percentage of CMC gum powder needed and the concentration of the gum solution. I just need to weigh the jar of glaze (without lid), weigh a teaspoon of the liquid glaze (lower left), dry it (upper right) and weigh the dry (lower right). After filling in these numbers the sheet tells me what weight to evaporate the jar to and how much gum solution to mix in. It paints on just like a commercial glaze. But don't do this. I made another spreadsheet online (link below) based on starting from dry ingredients, adding the correct amount of water and gum solution. Of course, you need a good mixer to do this.

I have 161 grams of stain. I need to mix it into how much clear glaze slurry?

I have 161 grams of stain. I need to mix it into how much clear glaze slurry?

Stain powders are expensive. I want to make as much glaze as I can from every gram of this red stain I have at hand. I have weighed a teaspoon of my clear glaze liquid slurry (recipe G2926B). I dried it out under a heat lamp and weighed it again (top left). I have filled those two weights, 8.9 and 4.74, into a spreadsheet I made. It calculates the proportions of water and powder in the glaze slurry. I have filled in "10" for the percent of stain needed. It is telling me I need to mix the stain into 3040 grams of the liquid glaze. That gives me about 5 pints of glorious bright-red dipping glaze. The dipping process enables me to apply it so much more evenly than I can do by paint-on methods (provided that I have the right specific gravity and thixotropy). And, I got this much glaze for about $50 worth of dry materials (vs. $20 for a pint of paint-on glaze).

Common dipping glazes converted to jars of brushing glazes

Common dipping glazes converted to jars of brushing glazes

These are cone 6 Alberta Slip recipes that have been brushed onto the outsides of these mugs (three coats). Recipes are GA6C Rutile Blue on the outside of the left mug, GA6F Alberta Slip Oatmeal on the outside of the center mug and GA6F Oatmeal over G2926B black on the outside of the right mug). One-pint jars were made using 500g of glaze powder, 75g of Laguna CMC gum solution (equivalent to 1 gram gum per 100 glaze powder) and 280g of water. Using a good mixer you can produce a silky smooth slurry of 1.6 specific gravity, it works just like the commercial bottled glazes. The presence of the gum makes it unnecessary to calcine the Alberta Slip.

Stains added to a base glaze can change its melt fluidity. Adjust the base.

Stains added to a base glaze can change its melt fluidity. Adjust the base.

At the top is a melt-flow GBMF test ball of a cone 6 satin matte glaze, G2934. Left bottom: 8% 6213 Mason Hemlock green stain added. The color is good but it is not melting as much and the surface is more matte. A solution is to adjust the base: employ a 90:10 or 80:20 matte:glossy blend to give it better fluidity. Right bottom: 8% 6385 Mason Pansy Purple stain added. The percentage of stain appears to be a little low and its surface is a little too matte. Again, blend a some glossy clear in the the matte base to shine it up a little.

Dip-glazing vs. brush-on glazing: Which gives the more even surface?

Dip-glazing vs. brush-on glazing: Which gives the more even surface?

This is a clear glaze (G2931K) with 10% purple stain (Mason 6385). The mugs are cone 03 porcelain (Zero3). The mug on the left was dipped (at the bisque stage) into a slurry of the glaze (having an appropriate specific gravity and thixotropy). The glaze dried in seconds. The one on the right was painted on (two layers). Like any paint-on glaze, it contains 1% CMC Gum. Each layer required several minutes of application time and fifteen minutes of drying time.

Commercial glazes may not work on your clay body

Commercial glazes may not work on your clay body

Left: Plainsman M390. Right M370 porcelain. The bottom two samples are a popular ultra clear commercial bottled glaze that costs about $13/pint. On the porcelain, it is crazing. On the red clay it is saturating with micro-bubbles and going totally cloudy and even a satin surface (it should be like the transparent above it). It is likely very high in boron and melting too early. Whose fault is this? No ones. This glaze is simply not compatible with these two bodies.

Brush-on commercial pottery glazes are perfect? Not quite!

Brush-on commercial pottery glazes are perfect? Not quite!

Paint-on glazes are great sometimes. But they are even greater if you know the recipe, then you can make more and make a dipping version for all the times when that is the better way to apply. Why is that better? Because you have a huge advantage over a glaze manufacturer: You already have clear glossy and matte base recipes that fit and work on your clay body. You can add the stains and opacifiers to these (with 1% gum to make them paintable) and make your own jars. Don't have base recipes??? Let's get started developing them with an account at insight-live.com (and the know-how you will find there)!

My clear glaze outside. Commercial white inside. But a big problem!

My clear glaze outside. Commercial white inside. But a big problem!

I know my outside glaze recipe fits this terra cotta. It does not shiver on sudden heating or craze on sudden cooling. And I have a gallon so I can dip-glaze the outside and it dries perfectly in seconds. But that inside glaze? It is under too much compression, so much so that it is literally forcing the piece apart (that crack exploded onto the scene with a loud ping a day after firing). But I do not know the recipe. And I had to paint it on in three coats. The painting was difficult and it took ten minutes to dry each coat. A better way to do a cover glaze would have been to simply add 10-15% Zircon to my clear recipe (I can even adjust if the added zircon lowers its expansion too much). To apply that would have been a simple pour-in and pour-out. Or I could make my own pint-jar of brush-on by using a mix of gum solution and water (instead of pure water).

Better to mix your own cover glazes for production?

Better to mix your own cover glazes for production?

Yes. In this case the entire outside and inside of the mug need an evenly applied coat of glaze. In production, it would not make sense to attempt this by painting. For these reasons: Cost, quality, convenience. The right pail has 2 gallons of G2934Y base with 10% Cerdec yellow stain: $135. Cost of jars with the same amount: Almost $300! And you have to paint them on in three coats with drying in between. The one in the pail is a true dipping glaze (unlike dipping glazes sold by glaze manufacturers that dry slowly and drip-drip-drip just like brushing ones). This one dries immediately after dipping in a perfectly even layer (if mixed according to our instructions). And a bonus: This pail can be converted to a brushing version using CMC gum.

Specific gravities on three commercial glazes might surprise you

Specific gravities on three commercial glazes might surprise you

The freshly opened transparent low fire glaze on the left has a specific gravity of only 1.34. Yet it is viscous because they add alot of gum. It needs three coats to be on thick enough and takes quite a bit of time to dry each one. When dipping, a very thick layer dries very thin. So when you buy this you are getting mostly water! Perhaps this is another good reason to mix your own transparent cover and liner glazes. The center Potter's Choice glaze, made by the same company, is 1.52. That is a much better deal. And it goes on nice and thick. The Celadon glaze on the right is lower, 1.46. So glaze manufacturers can make a very broad range of specific gravities work, they just adapt the percentage of gum to impart the viscosity they want.

Out Bound Links

  • (Materials) CMC Gum - GUM, Aqualon, C.M.C., C. M. C.

    C.M.C.

  • (Articles) Where Do I Start?

    Break your addiction to online recipes that don't work. Get control. Learn why glazes fire as they do. Why each material is used. Some chemistry. How to create perfect dipping and drying properties. Be empowered. Adjust recipes with issues rather than sta

  • (URLs) Creating a Jar of Brushing Glaze - Worksheet

    https://docs.google.com/spreadsheets/d/1XLPlIrW4tXnqAyowrE_P96OmbMfzEA-ggkYHcqBHtSU/edit?usp=sharing

In Bound Links

  • (Glossary) Glaze Layering

    In hobby ceramics (at low temperatures), layering of glazes for decorative effects has been commonplace for many decades. Potters have traditionally used dipping and pouring techniques, but in recent years they have increasingly adopted commercial prepared brush-on glazes for their stoneware pottery...

  • (Articles) Creating a Non-Glaze Ceramic Slip or Engobe

    It can be difficult to find an engobe that is drying and firing compatible with your body. It is better to understand, formulate and tune your own slip to your own body, glaze and process.

  • (Glossary) Bleeding colors

    Overglaze decoration (and often underglaze also) often bleed on the edges, especially brushstrokes. The higher the melt fluidity of the colored layer the more bleeding will occur, especially if the over or under glaze is also fluid. Cobalt colors are often more fluid and runny, that is why this prob...

  • (Glossary) Glaze Mixing

    Potters in affluent places in the world have increasingly adopted commercial brushing glazes as their glazing method of choice. These have some clear advantages but also some important disadvantages (especially related to whether they fit the body, the fact that their recipe is unknown so they are n...


By Tony Hansen




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