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| May 2026: We are continuing a major code rewrite. Please contact us if you find issues. Thank you. Monthly Tech-Tip from Tony HansenI will send practical posts like these (from thousands I maintain). No ads or tracking. The first email will provide one-click unsubscribe. Signup is being email-bombed by bots. For now, please subscribe inside your insight-live.com account. BlogCovia Nepheline Syenite (from Canada):Here is what it does from cone 3 down to 05
These SHAB test fired bars are 95% nepheline syenite (5% Veegum added). By cone 02 (bar stamped #4) is self-glazing and glass-like with a total shrinkage (plastic to fired) of 15% (less than some porcelains). At cone 03 (the #5 bar) the porosity is 3% (a stoneware). This is not an absolute indication of the materials' melting profile because of the Veegum, it behaves as a powerful flux and melting catalyst. Context: Covia Nepheline Syenite Tuesday 12th May 2026 Bisque temperature can make a big difference with fitting glaze at low fire
This is Plainsman Buffstone with G2931L glaze fired at cone 06. A hotter bisque not only produces a stronger body but also eliminates crazing (these specimens were glaze-fired one month ago). Firing the bisque just one cone hotter has transformed the ceramic into a denser matrix having a higher thermal expansion. That has the power to put the squeeze on the glaze, preventing it from crazing. Hotter bisque temperatures can be problematic as they reduce bisque absorbency (thus lengthening dip and drying time for the glaze slurry). But for low-temperature hobby ware this is not as much of a problem since glazes are gummed and dry slowly anyway. They are multi-coated for this reason (these were applied in two coats). Context: Earthenware Monday 11th May 2026 These two transparent glazes are opposites:In melt fluidity and surface tension
This cone 04 flow tester compares two commercial low-fire transparent glazes. Their different chemistry strategies are revealed by the shape of these melt flows. While 3825B appears to have the higher melt fluidity, it also has much higher surface tension. This is evident in the narrow, rope-like stream and the way the flow meets the runway at a high angle before pulling into a rounded bead. A, by contrast, spreads and wets the runway, meandering downward in a broad, flat and relatively bubble-free river. Context: Ulexite, High and low melt.., Surface tension differences between.., The perfect storm of.., Surface Tension, Melt Fluidity, Transparent Glazes, Terra Cotta, Glaze Blisters, Clouding in Ceramic Glazes.. Sunday 10th May 2026 The ultimate testing instrument to measure plasticity:A potter's wheel. With an experienced potter.
The left two leather-hard mugs were made from a 100% Lincoln 60 Fireclay (from Gladding McBean). By itself, the clay matures into a stoneware at around cone 8. While the pure material has a pleasant, smooth, soapy feel and can be thrown on the wheel, the plasticity is lower than that of typical pottery clay. The mug on the right adds 2% bentonite. That simple addition transforms it into a delight to throw! And only increases the drying shrinkage by about 0.5%. Context: Lincoln 60 Fireclay, A typical clay lab.., Plasticity Saturday 9th May 2026 How to make the engobe on the left run less?Add water! Then make it thixotropic.
The white slip on the left, L3685Z2, (applied to a leather hard cup) is dripping downward from the rim (even though it was held upside down for a couple of minutes!). Yet that slurry was very viscous with a 1.48 specific gravity. Why? Because it was not thixotropic. The fix? I watered it down to 1.46 (making it runny) and added pinches of powdered Epsom salts (while mixing vigorously) until it thickened enough to stop motion in about 1-2 seconds on mixer shut-off. But that stop-motion is followed by a bounce-back. That is the thixotropy. It is easy to overdo the Epsom salts (gelling it too much), I add a drop or two of Darvan to rethin it if needed. When the engobe is right, it gels after about 10 seconds of sitting, so I can stir it, dip and extract the mug, shake to drain it and then it gels and holds in place. Keep in mind, this is a pottery project. In industry, they deflocculate engobes to reduce water content. But a deflocculated slurry can still be thixotropic. Context: Epsom Salts, Creating a Non-Glaze Ceramic.., Thixotropy, Rheology, Engobe, Uneven Glaze Coverage Saturday 9th May 2026 Here is why Gillespie Borate crawls some glazes
This is a variation on the 50:30:20 cone 6 very fluid-melt pottery glaze recipe. I reduced the Gillespie Borate (GB) to 37% instead of the original 50% (thus bringing the B2O3 from 0.63 down to 0.5). My objective was to reduce the melt fluidity. But the crawling was so bad in this that it is almost unusable. The reason was not obvious until I fired a sample to 1550F and 1650F. At the former, the integrity of the glaze layer is great, but by 1650F it melts suddenly and does this. It is not difficult to see why these “puzzle pieces” with curled up edges might pull inward to create "glaze islands" characteristic of glaze crawling. This is happening even though the percentage of Gillespie Borate is lower. Not surprisingly, Ulexite mineral, which GB almost certainly contains, is also known for suddenly shrinking and melting. Context: Gillespie Borate, Gerstley Borate vs Gillespie.., Gillespie Borate is doing.. Thursday 30th April 2026 Instagram is just your street sign.But your website is the studio!
Yes, it is still possible to host a WordPress website on a 1GB Amazon EC2 free-tier server instance. But the method is new: ChatGPT answers every question, takes you step-by-step. A domain (e.g. mypottery.com for as little as $5) is yours and signals permanence, confidence. Instagram is built for quick scrolling, followers are "rented attention". But your website content stays where you put it, no algorithm decides who sees your work. It can explain, tell a story for each piece, teach, organize and classify. It can tell search engines what search terms you want to be found for (e.g. “pottery classes near me”). People can discover you. Install the Stripe and a shipping plugin in WordPress and your site can take orders, calculate shipping, make invoices, collect payment, provide tracking. And, a website lets you collect emails and contact and notify people directly. Context: An entire website created.., WordPress Thursday 30th April 2026 Joining rules are differentWhen clay is soft and plastic
This woman has quickly laid coils of smooth plastic clay on top of each other, in a conical shape. Then she simply begins throwing, centering, compressing and even verticaling the walls on the first pull. Since joining stiffer grogged clay elements, as done in typical hand-building, can be a time-consuming, elaborate process, how can this potter just ignore that? Context: The incredible plasticity of.., Tandoor Oven making How.., Video Throwing a large.., Clay Stiffness, Plasticity Tuesday 28th April 2026 Does this poodle belong in this team?Does the frit you use belong in your glaze recipe?
In industry it is normal to use frits whose chemistry is either unknown or approximate provided. The manufacturer has designed them for a specific use, so in many cases they comprise 80%+ of recipes used for that purpose. However potters more commonly use them as minor additions to recipes, they source needed oxides to the oxide formula (instead of raw materials). Context: Frit, Glaze Chemistry Monday 27th April 2026 DIY glazes can do something commercial ones cannot:Go on evenly, in one coat and dry in seconds.
Commercial brushing glazes are laced with CMC gum to make them paint on thin and dry slowly. Why would anyone want that? Layering. Brushing on layers takes time and it is difficult to get even coverage, but it justifies brushing up the prices also! Context: Layer slayers and jar.., Here is my setup.. Monday 20th April 2026 |