The trade is glaze recipes has spawned generations of potters going up blind alleys trying recipes that don't work and living with ones that are much more trouble than they are worth. It is time to leave this behind and take control.
Ceramic suppliers can’t sell their stocks of books anymore. We supposedly don’t need them because we are all binging on Google, YouTube, Facebook and Instagram ceramics. And recipes on Glazy. It’s exploding. A lot is good, but one issue that can waste so much time is the “trafficking of glaze recipes” that don’t work. Many studios are "bucket morgues" of failed tests (and the powdered materials bought to try them). People spend money to mix ridiculous, expensive recipes, ones that end up in the garbage. Are you still addicted, going again and again for more punishment? Or did you find one that works — sometimes? But punishes you all the others? Are you really learning anything?
More than ever, as a person that wants to understand glazes, how to formulate, adjust and fix them myself; I am marginalized. Lonely. As a ceramic culture we are getting more and more mentally lazy and wasting more and more money to make less and less technically acceptable ware. This article is a little disjointed and wandering, that reflects my lack of ability to step back far enough to understand fully what is happening to our craft and science.
Notwithstanding, there are gems out there to be found and adapted. But how can you find them while recognizing the time wasters? Ask yourself: 1: What do I need? 2: What do I want?
Let’s answer #1 first. In production or hobby ceramics you need a base transparent that fits your clay body, reliably fires crystal clear without micro-bubbles, does not craze or scratch or mark or leach, has good application properties, whitens with zircon and colors with stains. Likewise for a matte base. These base recipes, along with knowledge how to mix (control SG and thixotropy) and fire them are worth any effort to get. Not just because they can cover the functional surfaces and are well behaved but, as noted, the excitement of discovery can be satisfied by adding colourants, opacifiers and variegators. Or they can be coloured as a first coat on which to layer all sorts of commercial decorating products. Technically this may be all you need so you can stop reading here.
Admittedly you might have more specialized desires (e.g. a fluid melter, a low Al2O3 base for growing crystals). Or the color you want might require special chemistry in the base (e.g. significant BaO, presence or absence of ZnO or MgO, high levels of CaO). These are standalone recipes, exceptions to the base-with-additions approach. Are you really sure this is what you need? That the approach I described in the previous paragraph is not what you need? Could a simple stain addition to a base be all you need? Could you transplant the “mechanism” in the recipe that has caught your attention into your own clear glaze?
Ok, I get it. You really do need something special. First, don’t be naive, such recipes often come with baggage (like issues with crazing, leaching, hardness, running, consistency, application) so go in with both eyes open. So what is the best way to find one? Many people want a shortcut: throw the “google dice” and land directly on a reactive glaze that crystallizes, variegates, swirls and runs in rivulets, dances with wild colors or subtle effects that highlight every contour. Having no side effects! They want the buzz that kiln openings of such “street recipes” give. Unfortunately the real world is just not like this. The people who share them fail to describe all the details to follow to make them look like the picture. Or they do not understand what they are sharing. It’s those pictures that get us addicted and coming back for more punishment!
Consider some of the reasons why a glaze recipe might not "travel" very well.
If you are a beginner in ceramics you might reason: "Why would anyone post a recipe online if they know it does not work?". However (noting the above-mentioned) they likely do not know it does not work. Or they are unaware that their narrow circumstances are, by coincidence, an enabler for a small window in which it does do something they like. Or they have a different idea of what "working" really means, maybe emphasizing aesthetics, possibly to the extent of totally ignoring functionality and practicality. Misguided trust in online recipes can discourage newbies who cannot find success with them, blaming themselves. It can even go further: Some people, who confront failure in trying a recipe for the first time, actually blame specific materials in the recipe, flaming manufacturers online "who cannot keep their products consistent". This kind of thinking is misguided, even if it were true that a recipe depends on a material being absolutely consistent, that kind of fragile recipe would not be worth using.
Yes, there is something that travels even better than oxide formulas. It is the knowledge of what each oxide type contributes to a glaze, what each mineral type does to give it fired personality, and how they affect physical working properties. Each new recipe either confirms or fine tunes your existing oxide-effect knowledge, or educates you in the effects of its special purpose source materials (i.e. colorants, opacifiers, crystal forming agents) or unique formula (i.e. crystals from high CaO and low Al2O3 ). Each can be adapted to your own proven base 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 any more.
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 overgrazed. 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.
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.
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 make it paintable? 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.
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 brushing or base-layering versions using CMC gum.
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. This is misguided trust in trafficked recipes (ones with insufficient 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, glaze thickness are also involved. People who post glaze recipes like this often do not fully understand their mechanisms.
It contains significant Frit P-25, I googled that to Digitalfire, it contains 1.8% fluorine! When 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?
You need variable speed (not constant speed). Although some have timers these are not useful. The prices range from $100 to $thousands. They do not always come with the shaft and propeller (but it is easy to get a stainless steel shaft). A table-top device may be rated at 20L capacity, for example, but that is for thin liquids. For thick ceramic slurries it likely will only handle 8-10L (if the propeller is suitable). Question the RPM rating, the cheap mixers use stepper motors (they require minimal electronics) and only get a fraction of the claimed RPM. These will only be useful with a large propellor having steeply pitched blades. Buying a propeller is not practical because one will likely cost more than the mixer, be the wrong pitch, wrong direction, wrong size. 3D-printing one yourself is the best way (keep reprinting until it works well). If the shipping weight of the package is 15-20 lbs much of that will be the heavy metal base.
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. 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. See the article to find out.
They might look great on a fancy website, but what are the chances they will actually work in your circumstances? Very low. After trying many glazes you may think you have found one that works. But does it really? Or is it erratic and unreliable? Difficult to use. Does it leach or craze or shiver or pinhole or blister? Or give you other problems? Be critical and cautious about recipes you find.
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.
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.
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).
Orange is a very difficult color in ceramics. Inclusion stains are the only reliable method and universally used in industry. But you could ignore that and try a bunch of recipes online, buying exotic materials to complete each one. Maybe one will be orange enough, but will it craze or run or blister or leach or cutlery mark or crawl? Or you could put an orange stain into a transparent glaze you already know works on your clay. Or, how about trying a premixed orange at low fire? Ware can be amazingly functional and there are so many other bright colours available.
Melt fluidity test showing Perkins Studio clear recipe original (left) and a reformulated version that sources the boron from Ferro Frit 3134 instead of Gerstley Borate (right). The later is less amber in color (indicating less iron) and it melts to very close to the same degree.
Understanding your transparent glaze and learning how to adjust its melt fluidity, thermal expansion, color response, etc is a base on which to build all your other glazes.
This term refers to critical thinking ability that potters and technicians can develop to recognize recipes having obvious issues and merit, simply by seeing the materials and percentages.
Stop! Think! Do not get addicted to the trafficking in online glaze recipes. Learn how they work. Understand them. Then make your own or adjust/adapt what you find online.
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