This is a cone 6 oxidation transparent glaze having enough flux (from a boron frit) to make it melt very well, that is why it is running and pooling. Iron oxide has been added (around 5%), producing this transparent amber effect. Darker coloration occurs where the glaze has run thicker (because it absorbs more light). This simple mechanism enables the glaze to automatically highlight contours, emboss and textures on the underlying surface. This mechanism works with any color in almost any transparent base glaze, as long as bubble clouding and crystallization do not occur. Entire lines of commercial glazes (e.g. AMACO Celadons) are based on this mechanism and potters prize it (industry doesn't like it because it is difficult to achieve consistency).

This glaze relies on high levels of K2O and Na2O to produce the brilliant gloss, however the side effect of that is crazing. These are sourced by feldspars, nepheline syenite and are high in certain frits. To achieve this effect, recipes must rely on other fluxes like boron, lithium or zinc.

The more complex your supplier's supply chain, the more likely they won't be able to deliver. And that prices will rise even further. How can you adapt to disruptions, even turn them into a benefit? Historically, pottery has been a shining star of resilience and independence because the materials were in the ground nearby. You cannot likely head out to the nearest hill with your wheelbarrow to get clay, but you can do something even better.

Rather than viewing these containers as full of specific brand-name clays, minerals and man-made powders, it is better to view them as full of materials that supply the physical properties and chemistries needed to make bodies, glazes, engobes, slips, etc. By characterizing your glazes and bodies, using an effective record-keeping system, you can not only adjust recipes to adapt to changing supplies, but even improve them in the process (adjusting glaze thermal expansion, temperature, surface, color, etc). Or, use materials native to your area. It is not rocket science; it is just work and gradual learning accompanied by organized record-keeping, good labelling and interpretation skills.

As potters, we learned during COVID that no one is affected by supply chain problems more than prepared glaze manufacturers; they have complex recipes that require complex supply chains. It wasn't just availability; product consistency was also affected. It is again time to think about DIY, to start learning how to weigh out the ingredients to make at least some of your own. Arm yourself with good base recipes that fit your clay bodies (without crazing or shivering). Add stains, opacifiers and variegators to the bases to make anything you want. Admittedly, ingredients in your recipes can also become unavailable! But DIY as about options. When you "understand" glaze ingredients and what each contributes to the recipe and oxide chemistry, you are equipped to go well beyond weathering material supply issues. You will improve recipes, not just adjust them, to accommodate alternative materials. It is not rocket science; it is just work accompanied by organized record-keeping and good labelling.

Peggy-potter makes the hand-crafted mugs. Carla-coffee-drinker, needs a mug. This apparent perfect alignment goes off the rails when Carla compares Peggy's $50 price with premium imported mugs costing $5 (shown here). Especially when the imports emulate Peggy's techniques flawlessly while offering better durability and strength!

Peggy has to choose between hyping "kiln drops" on social or cutting costs. DIY techniques and supplies are a first option. Also mold-making and slip casting, even mixing her own casting slips. Mixing her own glazes, underglazes and engobes is the next step. Or learning to use less expensive bodies (e.g. with engobes).

Going DIY is not a big equipment investment. A plaster table, scale, mixing and batching table and a propeller mixer are the most important. And keeping good records (e.g. an account at insight-live.com). Following manufacturers on Instagram to see their glazing and forming techniques can help. Build throwing and drying skills by making hundreds of the same item. Consider: What you do affects other potters, prices cannot keep rising, or there will be no market.

Strips of the same glaze recipe, each containing different percentages of zircon opacifier, have been applied across both a dark-burning body and a white engobe. While it is difficult to measure the absolute degree of opacity from a photo like this, the side-by-side comparison makes differences easy to see. Tests like this demonstrate that simple visual comparisons can often be as useful as instrument measurements when evaluating glaze opacity. Colorimeters measure Lab* color values, not opacity directly. This test is really about visual hiding power, which instruments don't always capture well.

In this case the technician may be trying to determine how to achieve the required whiteness at minimum cost. Both the engobe and glaze contain zircon. The whiter the engobe the less opacifier is required in the glaze over it. Zircon is an expensive material, and reducing the total needed by even by 1% can make a significant difference in production cost.

The same test method can also be used to compare different brands of zircon opacifier in the same recipe.

A subtle aspect can be noted by coverage on the dark body: Opacity differences there become visible, whereas on the white engobe, differences almost disappear. Where an engobe is not to be used, an effective tweak is to add a thin black line under the glaze, then the lowest zircon level that hides the line becomes obvious.

Are your records in a messy binder? Binders don't have "Search" buttons. Side-by-sides. And many DIYers would generate a binder full in a year. But how does one even start to organize?

Start by moving your recipes to an account at insight-live.com, assigning each a code number. Then, in your studio/lab, label every fired sample, bucket, jar, glaze test, bag with the corresponding code number. Upload pictures for each recipe. Enter your firing schedules. Research the solutions to issues you are facing with glazes at the Digitalfire Reference Library (ask us questions using the contact form on each of the thousands of pages there). Then start planning improvements and tests. Choose a recipe you need to improve/evolve, duplicate it, increment the code number, make changes, enter explanatory notes. With this preparation you will hit the ground running back at work.

The mug on the left, #1, is a commercial brushing glaze. It is opaque enough to cover this red-burning clay body. It shows the desired effect. That depends on the fact that opaque glazes stretch thinner on the sharp edges of incised designs. If they have enough melt mobility and are applied right, the effect is amplified. This potter is attempting to mix her own DIY equivalent as a dipping glaze, adding 4% tin oxide to a transparent base glaze in #2 and zircon (a higher percentage) in #3. As you can see, the effect is not working as well, and there are several reasons:

#2 is whiter because it uses tin oxide as the opacifier (vs. zircon, likely used in #1). #2 and #3 have less melt fluidity; the base is likely G2926B. #1 was applied by brush, the others using a dipping glaze. Matching the original involves a combination of things: A base having more flux (especially B2O3) is needed (e.g. G3806C). Careful control of application thickness. The right percentage of opacifier. And, it may be necessary to mix the DIY version as a brushing glaze, that method of application might be needed to get the careful control of thickness and thickness variation needed.

Insight-live does not automate formula-to-batch calculations, but it does assist in doing them. And it provides the tools to create an audit trail of test results, pictures and notes and a path to document subsequent adjustments. Along the way, you gain material knowledge and intuition. In this example, we derive the recipe of materials needed to source the oxide formula of a zinc clear cone 6 glaze (sourcing the oxides needed using a Ferro frit and other common raw materials). We'll create the target in a panel, start the batch in a panel beside it, supply the B2O3 from a frit and then the fluxes from feldspar, zinc and whiting. Then finish by rounding out the Al2O3 and SiO2 from kaolin and silica. The picture below shows the panels, the original target formula on the left and the final derived recipe on the right. The derived transparent glaze is on the inside of the mug and the outside is G3875, another zinc clear with iron and chrome added to produce the orange.

This glaze is 85% Albany Slip and 20% Ferro Frit 3195. These bisque tiles were dipped in a brushing glaze version of it (just water and powder). The glaze is applied quite thin on the front tile and thicker on the back one. The material gelled slurries and required a lot of water to make them thin enough to use. For assured success, this or any glaze that had a high percentage required mixing the raw Albany Slip with a calcined Albany Slip (which people had to make on their own).

Oil-spot effects depend on being able to layer glazes. Normally, a black underneath and matte white over top. Using dipping glazes is obviously advantageous for this type of piece; the second dip covers the other half and creates the double layer needed. But dipping glazes contain clay in the recipe (almost always kaolin or ball clay), it satisfies multiple needs: It suspends the slurry, hardens the drying glaze, and supplies critical Al2O3 to the chemistry. The upper glaze here is a matte; so it needs extra Al2O3, which means it likely has extra clay. 20% kaolin (non-plastic like EPK, Grolleg, NZ) is about the maximum or the glaze will shrink too much when drying. If extra Gerstley Borate is added, then it will be worse. Drying cracks are the result when the fragile body-bond of the lower one fails to withstand the stresses of being rewetted and tugged upon by the upper layer being applied and drying. When the cracked double-layer begins to melt, it pulls itself into islands, leaving bare body between. That is called "crawling".

How to prevent this. Be smart about glaze layering and use recipe logic. The lower black can likely be adjusted to be a first coat dipping glaze. The clay content in the upper white one can be adjusted to reduce drying shrinkage (by splitting it between raw and roasted/calcined powder, or by using a clay having lower plasticity).