These two sets of SHAB test bars are fired from coldest to hottest (bottom to top) through the range from cone 04 up to cone 4. The graph shows the decreasing porosities and increasing shrinkages as temperature rises. Note the terra cotta reaches maximum shrinkage and minimum porosity at 2000°F (above which it begins expanding and melting). The talc body, by contrast, slowly matures, reaching a minimum porosity of 7% at 2150°F. It thus only sinters, never reaching a state of anywhere near the maturity and strength of the terra cotta. Clearly, the latter is not only high in iron oxide, but also in fluxes (like K2O, MgO, Na2O, CaO, etc) - these are responsible for how fast it vitrifies. The point where maximum fired strength is produced is the third bar up, 1970°F on the graph. However, there are multiple issues: Ware will warp in the kiln, the terra cotta red color has been lost and LOI gases of decomposition will disrupt glazes (with bubbles, blisters and pinholes). The most practical temperature is the second bar up, adequate density, good color, better quality glaze surfaces. The talc body? Although it fires to poor maturity across the range, it has one trump card: It provides a good base for glazes, producing bright colors and no bubbles.

G2926S reduces the thermal expansion of the popular G2926B (a durable, crystal clear, easy-to-use general purpose cone 6 base glaze for stoneware and porcelain). However, some porcelains (e.g. these Plainsman P300 mugs) need the lower thermal expansion this offers (to avoid crazing). This recipe adjusts "B" chemistry by adding low-expansion MgO at the expense of high-expansion KNaO (while maintaining gloss). This is more expensive to make (because it calls for Frit 3249 or equivalent) - use it if G2926B (with 325 silica) fails an IWCT test for crazing. These mugs were fired using the PLC6DS firing schedule, the S glaze was opacified with 10% Zircopax and the outside glazes are G2934Y silky matte with added stains. Need to reduce COE even further? Try G2926J.

This inside glaze is G2926B (on Plainsman M340). It is capable of firing glassy smooth, crystal clear and un-crazed even on coarse stonewares. Watch the video 📹 to see the four unusual things we do to get reliable glazes like this. But the recipe is only part of getting success. Mixing it as a thixotropic slurry is another. And the firing schedule: Look closely at the two glazed tiles. The bottom one, although fired lower (cone 5.5) was slow cooled using the C5DHSC schedule - note how much smoother the glass is (the upper one was fired to cone 6 using the PLC6DS schedule).

The outside is a floating blue, GA6-C. These are a dime a dozen but a good transparent is priceless. Did you know that the outside glaze can be made from the inside one by simply adding 2:4:1 iron oxide:rutile:cobalt oxide? This glaze can be stained, opacified and variegated in an infinite number of ways. And it is adjustable (e.g. lower thermal expansion, lower or higher melting).

These are the original cone 6 Perkins Studio Clear (left) beside our fritted version (right). You cannot just substitute a frit for Gerstley Borate (GB), they have very different chemistries. But, using the calculation tools in my account at insight-live.com, I compensated for the differences by juggling other materials in the recipe. I even upped the Al2O3 and SiO2 a little on the belief they would dissolve in the more active melt the frit would create. I was right - a melt-flow GLFL test comparison (inset left) shows that the GB version flows less. Using this on ware exhibited another issue (after doing a IWCT test): Crazing. The very good melt flow on my G2926A fritted version is thus good news: It can accept more silica - the more silica, the more durable and craze resistant it will be. How much did it take? 10% more! That ultimately became the recipe for our standard G2926B cone 6 transparent.

This is the G3914A recipe on Plainsman M340 test tiles. They were fired at cone 6 using the PLC6DS schedule. We tested them in four different caustic liquids (using the GLLE test), there is no sign of leaching on any of them. This recipe contains only 4% black stain, that is enough to stain the base GA6-B glaze to a jet black. The surface has a unique iridescence that is not found in any other glossy black we have used.

Wikipedia terms Knapping as “the shaping of flint, chert, obsidian, or other conchoidal fracturing stone through the process of lithic reduction to manufacture .. flat-faced stones.” In other words, it is the process of carefully breaking off pieces to create sharp edges and controlled surfaces.

Knapping is a thing. r/Knapping on Reddit has 12k followers. There are lots of YouTube videos, articles and books, websites and even commercial suppliers. Michael Slack has answered the question: Could Zero4 porcelain be knapped? The answer, as you can see, is: Nicely. This is not an arrowhead but a proof of concept biface. Michael was motivated after seeing the glassy internal structure of the fired material. He used 0.3% cobalt, thus the blue color. If you attempt this be advised of the importance of extremely vigorous mixing of the slurry to remove all agglomerates. Try various temperatures to find the most knappable material.

This is G2934Y (a version of the G2934 cone 6 matte base recipe that supplies much of the MgO from a frit instead of dolomite). Like the original, it has a beautiful fine silky matte surface and feels like it would not cutlery mark. But, as you can see on the left, it does! The marks can be cleaned off easily. But still, this is not ideal. The degree of matteness that a glaze has is a product of its chemistry. But can we fix this without doing any chemistry? Yes. By blending in some G2926B clear glossy (90:10 proportions). The result: The marks are gone and the surface is only slightly less matte. This underscores the need to compromise the degree of matteness, on food surfaces, enough to avoid staining and cutlery marking.

Multiple batches of fired test bars, organized by temperature, have already been weighed and measured (the weights and lengths are written on the sides of the bars). Each batch is accompanied by the cones from the firing in the test kiln (these influence how the temperature is recorded and adjustments to kiln firing schedules). Since we are working on many runs, tests and projects at any given time, these tests pile up rapidly. And they generate a lot of SHAB test data that needs to be input into your Insight-live.com account promptly.

This is a mold to test the shape and size of a Medalta Potteries ball pitcher. The shape and orientation of this 3D printed mold has worked better than others done till now for several reasons:
-It puts the printing artifacts where easily mitigated (e.g. centre of the belly). The steep slopes and verticals print smooth thus easing mold release.
-This 3D-printed shape is strong even though the walls are only 1.2mm thick.
-Th approach is conducive to a hybrid plaster and 3D printing approach: Making a case mold for the production of working molds.

Like the others, it retains several advantages intrinsic to this method:
-It is quite large yet each plaster half weighs only 2kg (4 1/2 lb) and dries quickly.
-Embeds were cast into the plaster enabling easy insertion of natches or spacers.

Plastic natches are cast into plaster molds to provide a durable and good-fitting interlock between pieces. The traditional self-interlocking 3/8" or 9.5 mm (nipple diameter) one has not proven suitable for mold making based on 3D printing. Our solution is a four-part system. To use it, your 3D printed mold shells only need matched 13.5mm holes.
-13.5mm holes in 3D printed case molds are all that is needed to adapt to these.
-3D printing case and block molds necessitates pouring plaster and rubber into shells with planar mating surfaces downward (they must sit flat on the table). The thin flanges on the clips cause minimal issues.
-Casting an embed into a mold enables gluing (or friction fitting) a natch or a spacer inside.
-The use of embeds permits flat mating surfaces - these can be sanded (for better flatness and fit). They also allow replacing natches if they get broken (assuming friction fit).
-A set of four interlocks (4 embeds, 4 clips, 2 spacers, 2 natches) weighs 8.7g.
Our drawing shows the measurements we use. 3D printing is precise enough that the inside dimension of the embed is the same as the outside of the natch shoulder, yet the natch fits. The same good fit happens with the clip and embed and the natch nipple and spacer (although it is necessary to chamfer the bottom corners and bevel the top corners of the spacer for better insert).
Some dimension changes may be needed to fine-tune for printing in your circumstances.