This is G2826A3, a transparent amber glaze at cone 6 on white (Plainsman M370), black (Plainsman 3B + 6% Mason 6666 black stain) and red (Plainsman M390) stoneware bodies. When the glaze is thinly applied, it is transparent. But at a tipping-point-thickness, it generates boron-blue that transforms it into a milky white. Glazes that are very glassy but on the edge of structural instability do this. So they are not good for functional ware.

This is an adjustment to the 50:30:20 Gerstley Borate base recipe (historically used for reactive glazes, often on functional surfaces! This cuts B2O3 and adds significant SiO2. But it still has double the boron of a typical functional glaze. While the chemistry of the original was within the territory of boron blue development (relatively low Al2O3), this one is better because of the increased SiO2 (the high MgO:CaO ratio is likely also helping). Boron blues like the lower Fe2O3 content or Gillespie Borate. One more factor: I am using 325 mesh silica here, it dissolves in the melt better.

Would you like to be able to use your own found-clays, ones native to your area or even your property, in your production? Follow me as we evaluate a mystery clay sample provided by a potter who wants to do exactly this. I will use ordinary tools that any potter either already has or can buy at low cost. We will describe this clay in terms of plastic clay bodies and common ceramic materials that most potters already use. The potter who submitted it has worked enough with the material to suspect it has potential and he wants to know how to best utilize it (e.g. at what temperature, with what glazes, mixed with what, processed in what way). In technical terms what we are doing is called "characterization".

This artisan, Dennis Cuku, is the king of DIY tile, making "actually HANDMADE" product using a red-burding terra-cotta-like middle temperature clay body. He also makes glazes in-house and fires using 36 shapes. He mixes 129 glazes and produces about 50,000 ft.² of tile per year. Tile making presents many unique challenges, not the least of which is the need for consistency and predictability of surface character and color. This endeavour is made possible with data, a lot of it. Not just glaze recipes, but many forming, glazing and firing procedures and techniques that must be documented.

Watch this 30-second video to see. Gelled (thixotropic) slurries for dipping are so much better to work with; you'll never go back once you have mastered this DIY technique. While some glazes and engobes gel naturally, especially those with high clay content, these almost always work best when the water content is within a certain range, so fine-tuning like this is still needed. Although not shown here, if over-gelling happens, a drip or two of deflocculant (e.g. Darvan) brings back the fluidity, this is more likely to happen with engobes since they need more gel (for dipping and even more for painting). A side benefit of this: No settling in the bucket.

These legacy slip casting molds from Medalta Potteries (made from 80 year old masters). They are difficult and time-consuming to use and produce less than optimal results because they have no top section (this no spare) and require constant filling during cast time. Demolding requires cutting the lip flat (top right). But a lot of time trimming and sponging is needed to round it again, but making the lip even and symmetric is difficult to say the least.

I found a way to make these molds easier to use and better: A 3D printed spare/pouring spout that also defines a rounded rim. It can be glued to the top of the mold with slip. Of course, the PLA print is not absorbent, but this still works because the mold top edge is able to dewater the slip even inside the contoured top it forms. The print also acts as a cutting guide to cleanly cut anway any clay inside the spout section, leaving a clean line inside the lip. And the shrinkage of the clay pulls the pitcher lip away from the print.

This page is dedicated to the skill and intuition of the Plant Technicians who kept the ceramic industry in North America thriving before the 1980s. Before we started clicking buttons to outsource things. They weren’t “role fillers” supplied by HR, they were “believers”. They understood everything in the plant; the equipment, processes, procedures, materials, recipes, kilns and firing. Managers set the pace, but the technicians made the pace possible. It was a time of local knowledge and company loyalty. They weren't temporary consultants or voices on a helpline; they owned and solved the problems. They were also mentors who passed their knowledge down.

These binders hold 40 years of recipes and techniques, kept by Albert E. Holthaus at Modern Art Products and Tierra Royal Potteries. Men like him were a legacy; they were the true "operating system" of a golden age of independence. They ensured the wheels kept turning, the fires kept burning and the quality kept enduring.

This batch-to-formula calculation was done by Albert E. Holthaus at Modern Art Products Company in Kansas City, MO (during the 1960s). Doing this not only seems quaint today, but suppliers put up roadblocks to doing it.

Notice that he took the manufacturer-supplied percentage analysis for each material (bottom) and calculated the unity formula for use in his batch to formula calculation (top). The recipe material weight amounts are missing in the latter; this appears to be his effort to create a documentation page of the recipe on the oxide formula level (this is what mattered to him). It was a time when frit formulas were published by their manufacturers. He also calculated the glaze's chemistry as a percentage analysis, likely to lay a basis to assess it against stated requirements from stain suppliers (certain stains only work when the host glaze chemistry meets a certain profile).

Doing this now is so much simpler. But almost no one actually does! The closest most technicians get to oxide formulas is choosing a frit from a list of ones for which the chemistry given by the manufacturer is only approximate.

This reduction stoneware glaze is producing white streaks on some pieces (left center). The body is a coarse iron stoneware. A magnification is needed to better explain this.

It is 2025, many smartphones now have dedicated macro lenses and can be held as close as a 1 centimeter. They automatically sense placement and switch to using the macro lens. Of course, the phone must be held rock steady and good lighting is essential. If you are a doubter of what they can produce, look at the two magnifications on the right. On the top one, the white streak is clearly visible, floating in a sea of phase-separated glass patterned by earlier-escaping bubbles. The extreme magnification on the bottom right appears to implicate tiny crystals growing in an area where late bubbles have escaped, changing the pattern of phase separation. This doesn’t yet explain the cause, but it is valuable information courtesy of a macro lens.

Place: Vernon, Alabama.
Story: Potter's friend sends a picture of an outcrop of white clay in the ditch near his driveway.
Result: A DIY claybody is born.

This planet is full of accessible clay deposits. Many can be used as-is for stoneware, earthenware and even porcelain. Characterizing this clay is the first step. How plastic is it? What does it look like when fired at different temperatures? Does it contain impurities that need to be sieved out? Does it dry without cracking? Does it work with glazes? Etc.

A journey of clay discovery to a finished piece is one of the most rewarding experiences you can have as a potter. And be more self-reliant. You don’t need special gear, just curiosity, eyes that notice, a few simple tools, and a willingness to experiment and learn to characterize clays. And one more thing: An organized way to keep records of your testing. Think of an insight-live account as a commitment to building experience; it is your memory of everything that worked. And didn't.

Or, more correctly, is this one a clay? The way I found out was to test it myself. That's what I did.

The giveaway of its marine origin is the tiny shells found on the sieve. The Cretaceous Sea once connected the Arctic Ocean with the Gulf of Mexico, covering the great plains of North America. Sedimentation left this deposit of Diatomaceous earth in central Alberta, Canada. This sample contains enough clay that I was able to slurry it up, dewater it on a plaster bat and then prepare SHAB test bars to try it at five temperatures. At cone 10 (bottom right) the porosity is 62%! And the LOI is 32% (others can go as high at 50%). Why? Raw diatomaceous earth contains physically bound interlayer water, it leaves by ~100–300 °C. It also contains structural hydroxyl water (in clay minerals or hydrated silica phases). This “chemical water” burns off between ~400–700 °C. And, organic matter from ancient algae, plants, or soil contamination also burns out between ~300–800 °C (as CO₂ and other gases). Finally, the carbonates (e.g. shells shown here) decompose around 700–900 °C, releasing CO₂. That alone can cause a big weight loss.

Note the test bars under it. Where this bar was sitting there is glassy deposit. What is that? Diatomaceous earth is mostly amorphous silica, but it almost always contains alkali and alkaline-earth impurities and sometimes boron. The latter can literally drain out, as a liquid. However here, the alkalis have volatilized (vaporized) or form alkali-rich fumes. These landed on nearby surfaces to react with the other test bars to form a thin alkali-silicate glass layer (similar to what happens in soda firing).