This is revolutionary because it is now practical to make one-off jigger test molds in one step using a consumer 3D printer and no plaster original model. Draw, print, glue, pour plaster, peel off (or heat off using a hair drier) the printed PLA piece by piece and you are ready to jigger test mugs.

3D design of this is simple: Sketch the outside profile of the mug and the mold, join them at the rim of the mug and then rotate. While the whole thing can be printed as one piece, print-time is drastically reduced by doing them as separate pieces and gluing. It is also best to print the step section of the mold much thicker to guarantee roundness for fit into the cuphead or ring. Printing the base of the mug separately is most advantageous, that eliminates the need for generating support and enables doing multiple iterations of embossed designs or logos. Printing a small inside ring to hold it in place for glueing is a also good idea.

Black-burning bodies are popular with many potters. This one is stained by adding 10% raw umber to a buff-burning stoneware. Umbers are powerful natural clay colorants, they have high iron and also contain some manganese oxide. Could a white engobe produce a porcelain-like surface on such a clay body? Yes. L3954B engobe was applied during leather-hard stage to this Plainsman Coffee Clay mug (on the inside and partway down the outside). After bisque, transparent G2926B glaze was applied inside and GA6-B outside. Notice the GA6-B over the engobe fires amber but over the black it produces a deep glossy brown. The engobe was mixed into a thixotropic slurry, as explained on the page at PlainsmanClays.com (see link below), and applied in a relatively thin layer. This porcelain-like result is a testament to the covering power of a true engobe. It is no wonder they are so popular in the ceramic tile industry - a red burning body can be turned white as a porcelain, that enables all the marvellous glazing and decorating they can do.

Yes. If it is a true engobe. This is L3954B fired at cone 6 on Plainsman M340S, it is fire-shrinkage-fitted to this clay body and opacified with Zircopax. The cover glaze is G2926B transparent. The opacity that this engobe is able to achieve here is because it is vitrifying to the same degree as the body, no melting is occurring and that is why it is completely opaque (even though it is applied as a very thin layer at the leather hard stage). This same performance could be expected in reduction firings to block the iron speckle (using the L3954N and variations recipes).

This is a cone 10 glossy glaze. It has the chemistry that suggests it should be crystal clear and smooth. But there are multiple issues with the materials supplying that chemistry: Strontium carbonate, talc and calcium carbonate. Each has a significant LOI and produces gases decomposition. When the gases need to come out at the wrong time it turns the glaze into a Swiss cheeze of micro-bubbles. A study to isolate which of these three materials is the problem might make it possible to adjust the firing to accommodate it. But probably not. The most obvious solution is to just use non-gassing sources MgO, SrO, CaO and BaO (which will require some calculation). There is a good reason to do this: The glaze contains some boron frit, that is likely kick-starting melting much earlier than a standard raw-material-only cone 10 glaze. That fluid melt may not only be trapping gases from the body but creating a perfect environment to trap all the bubbles coming out of those carbonates and talc. All of this being said, a drop and hold firing schedule could also smooth it out a lot.

These enable pulling apart the top halves of our ceramic beer bottle molds while the leather hard bottle is still embedded into the base. Starting upper left and clock wise:
#1 The 3D design for making a rubber case mold.
#2 It has been 3D printed in three parts (which are then glued together).
#3 PMC-746 rubber was poured in and the 3D printed parts were peeled off.
#4 Natch parts have been 3D printed.
#5 The embeds have been rubber cemented onto the rubber mold (to hold them in place during casting).
#6 Plaster was poured in.
#7 The plaster working mold has been extracted from the rubber, the embeds firmly rooted in place.
#8 The slots have been epoxied in place (lined up and positioned accurately so the natches hit the end of the slots just as the halves contact).
Centre: The mold partly assembled.

This was done in Fusion 360.
1: A make a sketch of a box, around the handle, on the XY plane. Offset that outward by 1.2mm (my printer prints 0.4mm wide, three passes give good strength).
2: Extrude to create box 1: The base backward by 1mm and the sides forward by 20mm.
3: Use five sides of the box as cutting planes to slice it out of the mug.

At this point I could print this in PLA filament, pour plaster into and then use a hair drier to peel it off. But let’s make rubber molds instead.

4: Move the box-with-handle away from the mug. Pull the four sides out by 5mm to thicken them.
5 & 6: Create box 2 around the outside of it, as a new body, 1.2mm wider and taller, 1mm more frontward and 1mm less backward.
7: Use box 1 as a cutter to remove material from box 2 and then pull the outer 1.2mm sides 5mm backward.
8: Shell out the back side to 1.2 wall thickness and make two 9.4mm holes (to accommodate natch clips).

To make side 2 mirror-image a new body using the front or back as the reflexion plane. The back side is then filled with PMC-746 rubber to make the block mold. Plaster is poured into that to make each working mold.

My objective was to continue skipping the making of a rubber case mold and 3D print them directly. Since 3D printed surfaces naturally part well from plaster and the artifacts, although visible, do not show on the final fired pieces, I even wanted to do this whole process without any sanding or oiling. However, despite printing a dozen or more variations, carefully controlling plaster/water ratios and waiting/mixing the recommended time periods, few good plaster molds were extracted without corner-breaking. Even painting the inner surface, oiling over it and beveling corners did resolve this issues. It seems that a combination of the printing artifacts, sharp corners, the handle perpendicular (because of the oval cross-section) and the inside negative shape all enabled the plaster to get a very firm grip on the PLA print. Although I could have resorted to a heat gun to soften the PLA material enough to pull it away I relented and decided to switch to making a block mold (for rubber) rather than a case mold (for plaster).

The problem is a combination of the shape and the degree of vitrification this body reaches. Polar Ice porcelain has to vitrify enough to achieve translucency, that means it literally softens - not enough to fall down but enough to warp out of shape given the opportunity. A sagging kiln shelf, for example, will produce a "rocking chair bowl". A non-stable shape will do the same thing. This piece was likely made by rolling a plastic clay slab and draping it down over a bowl-form, adding a foot ring, allowing it to stiffen and then uprighting it to dry. In this case the foot ring was too small creating an extreme overhang. Had the foot ring been wider and deeper it would have enabled the rounded inside contour, provided support for the outer section and minimized the overhang. If a small foot is really needed then pieces would have to be supported by donut-shaped setters sized and positioned correctly (and the outside would have to be unglazed). Or, it would have to be bisque fired, and supported, at cone 6 and then glazed at low temperature.

These three melt flows and mugs were fired at cone 6 (using the C6DHSC firing schedule). The benchmark recipe is 80% clay and 20% Ferro Frit 3195 (our standard GA6-B recipe).
-The center melt flow (and matching buff stoneware mug below) employ the original Albany Slip.
-The one on the right employs Alberta Slip. Notice that, although having a very similar melt flow, it needs an iron oxide addition to darken the color (e.g. 2%).
-The one on the far left uses an Albany Slip substitute made from 80% Redart, 6.5% calcium carbonate, 6.5% dolomite and 6.5% nepheline syenite (our code L3613D). The chemistry of RedArt is different enough from Albany that some compromises were needed to avoid over-supplying the iron even more (and firing darker yet). Although this Redart version runs in a very similar pattern on the melt flow, the character of the glaze on the mug reveals it needs a little more melting (increasing the frit percentage would take care of that).

#1: I got it in a foot-thick layer in a gravel pit in Leader, Saskatchewan (half way up the slope). I code numbered it L3822.
#2: The two lower bars are L3822, fired at cone 1 and 2 (at cone 2 the center Aero-chocolate textured material bursts out). The upper bars, 3822A, are a 50:50 mix with Pioneer kaolin (also cone 1 and 2).
#3: L3822A fired at cones 04,03,02,01,3 (top to bottom).
#4: 90:10 mix of M2, the mid-temperature red burning material Plainsman Clays uses, and L3822 (Cone 06,04,03,02,01 bottom to top). The 10% addition supercharges the M2 plasticity beyond what is practical to dry.
#5: The pure material, leather hard mugs (with exceptionally thin walls (because it is so plastic).
#6: The pure material cracks, only one of the 50:50 mix survived drying (even though they were dried over a period of weeks).
#7: Bisque fired 50:50 and pure material mugs.
#8: Cone 6 mug of the 50:50 mix. Notice it gases and clouds the clear glaze.
What is this clay? It is not a balanced material, but highly bentonitic. With lots of fluxes (like KNaO, CaO, MgO), it matures below what is possible with mixes of feldspar and kaolin. Its super fine particle size (and thus high surface area) enable imposing its maturity (even when mixed with a refractory material like kaolin). Treating this as a bentonite seems best, adding no more than 5% to improve body plasticity. Notice that it fires to a much nicer surface than the commercial raw bentonites shown below.