Trafficking in Glaze Recipes

Add a smattering of line blending and trial and error adjustment, and you can make anything you want; adjust it any way you want. You can tell the glaze what to do. So why jump through hoops trying to pacify temperamental recipes that are always throwing tantrums in your kiln? You don't have to put up with that anymore.

Related Information

What has the trust in online recipes come to?

These tests of a recipe called "Strontium Crystal Magic". The potter tried it on different bodies and firings. But instead of producing the magic crystals like the pictures, the surfaces fired totally matte. Reasoning "why would anyone put a recipe on line that does not work", she blamed one of the materials. Others fed that with rumours of claimed issues in its consistency. Admittedly, this glaze is meant for layering over others - but the source did not say that. This underscores misguided trust in trafficked recipes that most often lack sufficient documentation. Crystal glazes, by necessity, need to have a high melt fluidity. The crystals develop best with a specific cooling curve having a controlled fall at a narrow temperature range. Cool faster, they don't grow, slower and they matte the entire surface. Other factors, like clay body and glaze thickness are involved. People who post glaze recipes like this often do not document them well because they do not fully understand their mechanisms.

Tried and True recipes. Really?

Books and web pages with flashy pictures are the centrepiece of an addiction-ecosystem to recipes that often just don't work. Maybe these are "tried" by a lot of people. But are they "true"? Most are so-called "reactive glazes", outside normal practice - to produce visual interest they run, variegate, crystallize, pool, break, tint, go metallic, etc. But this happens at a cost. And inside special procedures and firing schedules that need explaining. It is not obvious these are understood by the recipe authors or sharers. And these recipes are dated and contain troublesome and unavailable materials. We use frits now to source boron. Stains are superior to raw colorants, even in glazes like this. Many of these will craze badly. And many will not suspend in the bucket. And will run during firing. Reactive glazes have other common issues: Blistering, leaching, cutlery marking, fuming. Trying colors in differing amounts in different base recipes is a good idea. But the project is most beneficial when it shows color response in terms of quality recipes of contrasting chemistries. The point of all of this: Understand a few glazes and develop them, rather than throwing spaghetti against the wall hoping something sticks. Commercial reactive glazes are an alternative also.

Want bright orange? Use a stain in your own base transparent recipe.

Orange is a very difficult color in ceramics. Inclusion stains are the only reliable method, they universally used in industry. But you could ignore that and try a bunch of recipes online. When they are presented on flashy web pages they can look tantalizing. But beware! Are the exotic materials you need to buy worth it. Will it actually fire orange? Will it craze or run or blister or leach or cutlery mark or crawl or settle like a rock in the bucket? It is much better to put an orange encapsulated stain into a transparent glaze you already know works on your clay. Then just experiment with percentage to get the color you want. Or, how about trying a premixed orange at low fire? Ware can be amazingly functional at low temperatures (e.g. cone 03-02) and bright colours labelled for cone 06 mostly work fine in that range.

Is that recipe you found online really what you think it is?

It contains significant Frit P-25, I googled that to Digitalfire, it contains 1.8% fluorine! When much of that gases off during firing are you really equipped to deal with fluorine gas in your studio? One answer is to substitute my own frits (which of course do not contain fluorine). I did the calculations in my account at insight-live.com (see the recipes side-by-side). In the formula, I substituted the F (fluorine) for a mix of CaO/MgO. In the recipe, I substituted Ferro Frit 3110 (it is also a high-sodium frit) for the P-25, then I juggled the rest of the recipe to match up the oxides. More Gerstley Borate supplies the lost B₂O₃, more ball clay supplies the lost Al₂O₃ and less silica is needed (because the ball clay brought along more). I ended up with a recipe that is going to suspend much better (more clay) and was able to eliminate the whiting (because the rest of the new recipe is supplying more CaO). This recipe has a high thermal expansion, that means crazing. Would it not be easier to simply add a red stain to a clear glaze you already have that is working well on your clay bodies?

The fact that it applied like this was not worth mentioning?

Recipes trafficked online seldom include important information. How could the author of this one not mention this problem? The slurry turns to a gel and fills with bubbles. And then you have to add water again. The extra water makes it shrink more, compromising the bond with the bisque so it peels away when overglazed. Later more water is needed because it gels again. After that it cracks on drying and the glaze crawls on firing. Is this really worth it? Actually, this recipe is fixable, the material at fault can be substituted (using a little glaze chemistry) to produce a much easier-to-use slurry.

The traffic in glaze recipes may burn your success!

Do you mix your own recipes? That's great, but the right approach to DIY is important. Online recipes might look great on a fancy website, but what are the chances they will actually fire the way they look in the picture? Or work in your circumstances? Did the contributor know the mechanism or give any sort of directions or cautions? After trying many glazes you may think you have found one that works. But does it really? How does it hold up to limit recipes? Does it have a balanced chemistry? Is it erratic and unreliable in firing? Difficult to use? Does it leach or craze or shiver or pinhole or blister? Or make you endure other problems? Be critical and cautious about foreign recipes. Most often it is better to find a base recipe, adjust and perfect it to your clay body, then add colorants, opacifiers and variegators.

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.

Popular white engobe recipe that does not work at cone 6

This is Odyssey slip, a engobe recipe that is trafficked on the web. It is recommended for low, medium and high fire ware. It is 30% Ferro Frit 3110 and 70% ball clay. This is a bi-clay strip, a sandwich of two plastic clays rolled into a thin slab and cut into a bar (to make the bar the Odyssey slip was dewatered to typical pottery clay stiffness). We are looking at the engobe side of an EBCT test (the other side is Plainsman M390). During the latter stages of the firing the engobe has begun to melt and blister and darken in color (which it should not be doing). During earlier stages of firing this engobe would certainly have had a higher shrinkage and would have bent the bar its way. But it is now bent the other way. That means the engobe could well be under compression (having a lower thermal expansion than the body). Or the body could simply have pulled it the other way when the engobe lost its rigidity. Either way, the engobe does not fit this body at this temperature.

Glaze recipes online waiting for a victim to try them!

You found some recipes. Their photos looked great, you bought $500 of materials to try them, but none worked! Why? Consider these recipes. Many have 50+% feldspar/Cornwall/nepheline (with little dolomite or talc to counteract their high thermal expansion, they will craze). Many are high in Gerstley Borate (it will turn the slurry into a bucket of jelly, cause crawling). Others waste high percentages of expensive tin, lithium and cobalt in crappy base recipes. Metal carbonates in some encourage blistering. Some melt too much and run onto the kiln shelf. Some contain almost no clay (they will settle like a rock in the bucket). A better way? Find, or develop, fritted, stable base transparent glossy and matte base recipes that fit your body, have good slurry properties, resist leaching and cutlery marking. Identify the mechanisms (colorants, opacifiers and variegators) in a recipe you want to try and transplant these into your own base (or mix of bases). And use stains for color (instead of metal oxides).

Frit made this Gerstley Borate glaze much better

This is a GBMF test, it compares the melt fluidity of the Gerstley Borate based cone 6 Perkins Studio clear recipe original (left, our code number G2926) and a reformulated version that sources the boron from Ferro Frit 3134 instead (right, our code number G2926A). The latter is less amber in color (indicating less iron). The good news was that it melted so much better that we were able to add significant Al₂O₃ and SiO₂ to really drop the thermal expansion (improving glaze fit on common clay bodies), which produced our G2926B base recipe. Every time I use it I think of how unfortunate we would have been had we continued to use the Gerstley Borate original.

I improved a cone 6 transparent glaze by removing the Gerstley Borate

The green boxes show cone 6 Perkins Studio Clear (left) beside an adjustment to it that I am working on (right). I am logged in to my account at insight-live.com. In the recipe on the right, code-numbered G2926A, I am using the calculation tools it provides to substitute Frit 3134 for Gerstley Borate (while maintaining the oxide chemistry). A melt-flow GLFL test comparison of the two (bottom left) shows that the GB version has an amber coloration (from its iron) and that it flows a little more (it has already dripped off). The flow test on the upper left shows G2926A flowing beside PGF1 transparent (a tableware glaze used in industry). Its extra flow indicates that it is too fluid, it can accept some silica (see the G2926B recipe that adds it and switches it to 325 mesh). This is very good news because the more silica any glaze can accept the harder, more stable and lower expansion it will be. You might be surprised how much it took, yet still melts to a crystal clear.

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. For hobby this makes sense. But in production cover brushing makes less sense. The right pail has 2 gallons of G2934Y base with 10% Cerdec yellow stain: $135. Cost of brushing jars with the same amount: $600+! And each jar logs 10-15 minutes painting time plus waiting between coats. The one in the pail is a true dipping glaze (unlike many commercial ones that dry slowly and drip-drip-drip). 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 brushing or base-layering versions using CMC gum.

Here is a good start to doing serious ceramic production at home

This is what you need to be independent, to create your own manufacturing company in your garage in 2021 Some of the prices are "instead of" rather than additive. There are many approaches to glazes, the more you are willing to learn the better you will be able to make your own (and save a lot). We recommend the cone 6 range using a small test kiln (like this 220v ConeArt GX119, don't scrimp on this, go for quality and the practicality of a Genesis controller). A kiln you can fire often and inexpensively is a key enabler to learning, developing techniques, products, designs, durable and decorative surfaces, solving problems. It can be fired multiple times a day. And it is big enough for mugs and similar sizes. It will get you into the habit of using some of your creativity for experimenting. It will give you the successes early on that will inspire you to press on learning. When you are ready, then get a big kiln and hit-the-ground-running. This potter's wheel is the best available and will last a lifetime, these often appreciate in value over time. And, build yourself a good plaster table. You will use it constantly. Not shown here is a propeller mixer, also an important tool. And you will need a sink equipped with a sink trap (Gleco Trap).

My head was in the clouds and I appreciate the grounding!

She was searching for a a matte, mottled white, rustic. For functional surfaces. And it contained this frit. The source from which she got it did not mention the barium content. Barium is certainly not a requirement to achieve a matte surface at cone 6, there of lots of ways to do it. And there are multiple matte mechanisms that can be exploited.

Trying to avoid knowing anything about glaze chemistry? Be ready for drama!

Maybe you don't think it is necessary to know anything about glaze chemistry to be a potter. Or a technician at a production facility. This thinking depends on how much mystery you mind tolerating. Because the reason for many of the problems you will encounter with glazes relates fundamentally to their chemistry. Perhaps you have other "social" actors in your sphere who also specialize in the "know as little technical stuff as possible" mindset. Who treat glazes like acrylic paint that comes in tubes - it is just color! From these people, you will get buying advice on expensive jars of tacky-looking "goop" that you have to laboriously paint on in layers. Or it will mean you'll be more likely to get trapped on the recipe treadmill, addicted to the traffic of recipes that never seem to work.

The first of 15 "Fool-Proof Recipes" wrecked my kiln shelf!

This is recommended in the booklet "15 Tried and True Cone 6 Glaze Recipes". This melt flow tester compares it with a typical cone 6 glossy, G2926B. This recipe is 90% Frit 3110 and 10% kaolin and their booklet recommends adding stains to it. But anyone knowing a little about this frit knows it would run off this flow tester even before bisque temperatures. It is crazy to recommend this. Even as a crackle. For cone 6 it needs to be diluted much more, not just with kaolin but also silica. I knew this would run but I underestimated its melt fluidity. I put a large tile below the tester to catch overrun, yet the melt ran off that and a big blob melted through the kiln wash and so far into the zircon shelf I could not chip it off! I cannot imagine how many people have tried this on vertical surfaces and had the same thing happen. The lesson: Use common sense when looking at recipes, then you don't even need to waste time testing them. Even if their authors did not!

Knowing about recipe limits could save you the work of testing this glaze

This is an example of a recipe being trafficked online that raises red flags just looking at it. Before dismissing the following I can tell you that I deal with hundreds of customer glaze issues a year and people expect recipes to work as shown if no documentation is included, many also assume functionality.

The first red flag: There is no silica! That means this is a low fire glaze masquerading as middle temperature, so it is going to run during firing (run a lot). It will also mean poor durability. There is a ton of feldspar, that means a high level of sodium. Without low-expansion MgO to counterbalance its high thermal expansion the glaze is likely going to craze badly. The mechanism of the crystallization is titanium over-supply, this has triple the maximum I would ever put in a glaze. The crystallization happens during cooling in the kiln (producing the visual effect being sought). But the the surface produced will cutlery mark and stain, probably very badly. Given the unbalanced chemistry this has, any colorant added will likely be leachable! I tested it and all my fears were realized. My slow-cool firing made the surface so dry it was very unpleasant to touch. Maybe this needs fast cooling. But who knows, there are no notes. This does not appear to belong on any functional ware, inside or outside. Someone noted that people use this to produce layering effects (see links). That begs documentation on how that wold work. Without gum would it lift and crawl as layers are added over it. Would you have to overlay every square inch? Would it still craze? All the how-to information needed to make it work are more important that the recipe itself.

Is the N505 cone 6 matte glaze recipe what you think it is?

This recipe is from page 2 of the booklet: "15 Tried & True Cone 6 Glaze Recipes". Click the following code, G3955, to see more information on how it compares with G2934 and G1214Z1 mattes. This flow test and these test tiles were in the same kiln, fired at cone 6 using our PLC6DS schedule. The defining characteristic of N505 is its extreme melt fluidity - it runs because it is overtired at cone 6. Still, the surface on the tile (lower right) is arguably more interesting than G2934. Some felt pen marking reveals why: The micro surface is much rougher. To its credit, although it does stain easier, it can still be cleaned with effort.

From the chemistry, shown on Insight-Live side-by-side screenshot. It has very low Al₂O₃ and SiO₂ - that turns on some red and yellow lights. One could hope to have melt fluidity and great functionality, but they pretty well never go together. This glaze should fire glossy - the 6% magnesium carbonate is the mechanism of the matteness - MagCarb is super refractory, it may not be dissolving in the. melt. The glaze should cutlery mark (although it seemed hard in our testing). Most important, low Si:Al levels always carry the risk of leaching - exercise caution adding any significant percentage of heavy metal pigments. Crazing is another possible issue over melted glaze.

Michael Cardew might be turning over in his grave!

This post got a lot of negative reaction on social media. To be clear, I work both sides of the fence, making my living on selling prepared glazes and clay bodies but I get my satisfaction being closer to the materials and processes. That is what enables me to give customer support. I am not an artist, ceramic art is outside the scope of this page. For part of my life in the craft of pottery I am also guilty of what I lament below. In all my years dealing with customer traffic at our store I have never once had a customer that was offended by seeing new clay and glaze recipes we are discovering in the studio and lab, that are better and cheaper than prepared ones. But online some are somehow offended by what follows. 80 manufacturers are selling convenience and encouraging disconnection - although I work for one of them I am a voice of caution about this.

This book was once a “Bible” of hobby and professional potters. They were independent and resourceful. They made their own clays and glazes, knew the materials, built their own kilns. Now we scan social media sites for ideas on layering expensive prepared goopy brushing glazes and hope they melt together into something presentable. Many have even forgotten how to wedge clay properly. We describe processes using mystical art language and exchange likes and poor advice on social media. Those who still know how to retotal a recipe and venture into mixing their own often end up in the online trafficking of an endless parade of recipes that don’t work. Now we even outsource design to AI. Even Nigeria, the very country about whom Cardew wrote, has lost its pottery tradition.

I never appreciated the book back there. Even though he came to visit us in 1973. I have always just taken whatever clay I needed out of our warehouse, but now that I very often make my own clay it really resonates. I got this copy on eBay, I value it as an inspiration to be more closely connected with the planet and the minerals it gifts us (of course I would not do everything as he does). He was no dinosaur, he understood and taught glaze chemistry and material mineralogy, his work was the basis for many prepared glazes we buy today. "Progress" is defined by some as convenience products that make modern ceramics easy. But I believe that, for many, progress is arming yourself with a little more understanding - it enables making better quality ware, in less time, for less expense and time than with prepared products.

Links

By Tony Hansen Follow me on

Got a Question?

Buy me a coffee and we can talk