This is part of a test hybrid case mold for a Medalta Potteries ball pitcher. The bottom plate is 3D printed and the top form is solid plaster. Recessed holes in the back of the plate enable securely inserting screws into threaded anchors embedded into the back of the plaster form. The upper plaster surface has artifacts (stair-casing remnants) from the 3D printed shell used to cast it. While these could be sanded out, we find that a flexible metal rib works much better. Even better than that is this custom 3D printed rib that I made, the edges are sharp and precise. I designed it with contours to match the belly, neck and rim of this piece. Using this, it takes minutes to smooth out the surface.

I have had a dream of being able to slip-cast jars with this type of fastener. Until this week, I did not even know what they are called or anything about their history. Now I do.

The first step was to design and 3D print a prototype. After three iterations, I found the best measurements for these bails, for use without a silicone or rubber sealing ring, to be 19.5mm vertically between the rings, a lid ring seat diameter of 79mm and a rim ring seat diameter of 87.5mm. It is going to be a challenge to create slip casting test molds to make jars out of ceramic instead of glass - the latter does not shrink out of the mold while clay has both drying and firing shrinkage. That being said, 3D printing enables quickly changing a mold design and size, reprinting in PLA and remaking a plaster mold. 3D printing also enables making holders, cutters and jigs to tool the diameters precisely at the dry stage. After that, precise firing along with monitoring of clay firing shrinkage should enable success. After that: Embossed designs cast into the flat walls.

G2917, which I mixed as a brushing glaze, is on the right. This is not sold in jars, I make my own labels as part of the demonstration that it is possible to make your own brushing glazes (ink-jetted onto regular paper, cut 62mm wide (2 7/16") and held securely on with 2 7/8" transparent packing tape). This glaze is less runny but lacks some of the floating white colouration. But that can be achieved using Alberta Slip floating blue L4655, it employs titanium instead of rutile (and relies on the rutile/iron mechanism for the blue color).

This spoon was dipped into a ceramic dipping engobe, L3954B. It contains no CMC gum, it was only flocculated using powdered Epsom salts. Without the Epsom salts, the engobe runs off, leaving only a film. But, when turned into a thixotropic slurry, it stays on the spoon in an even layer (as a gel), then hardens as it dewaters (left) and finally dries completely (right). With no cracks! It also fires to cone 03 with no cracks. Of course, if this were fired high enough, it would begin to shrink, crack, crawl, melt and then craze, ceasing to be an engobe. Of course, special low-expansion frits and additives and mixing, preparation and application techniques make enamels, which do melt, possible for metals.

This is M340 stoneware fired to cone 6 using the C6DHSC schedule. The L3954B engobe fires deep black (it has 10% Mason 6600 black stain). The engobe was applied by pouring and dipping at leather hard stage (inside and partway down the outside). After bisque firing, the piece was glazed inside using the base GA6-B Alberta Slip amber base. The outside glaze is Alberta Slip Rutile Blue GA6-C (you are seeing it on the bare buff body near the bottoms and over the black clay surface on the uppers).

The blue line is a crystal glaze firing schedule. While it reaches the same temperature as a typical glaze firing (purple line) it is different in how it does so. Notice key differences (while cone 10 is most common for this type of glaze, we will discuss theoretical differences in a cone 6 version):
-The steep climb: Crystallization needs a clean bubble-free melt, no lingering in temperature zones where they might start prematurely.
-The steep drop to 2000F: Crystals typically grow during a long soak in the 1900–2000°F nucleation zone.
-If the temperature is simply held steady at 1950°F only one type and size of crystal would form, likely smaller and crowding out others. The ups and downs are about manipulating the thermodynamics and kinetics of crystal formation — nudging new crystals to form or existing ones to grow differently.
-Cooling and then raising the temperature in the nucleation zone can re-dissolve smaller crystals or unstable nuclei. Then, cooling again encourages new crystal nucleation, rejuvenates existing ones or even changes the pattern of their growth.
-In the upper range of the nucleation zone, faster diffusion produces larger, more spread-out crystals. In the lower range, slower diffusion produces smaller, tighter crystals or detail-rich growth.
-Crash-cool to finish: Drop melt viscosity quickly to halt all crystal formation - this preserves a clean background and prevents blurring of crystal edges.
Crystalline firings are about precision and timing: Get in fast, melt everything, play within the range where crystals want to grow to get the type, distribution and size you want - and then get out. It is not difficult to see why crystal glazers may do thousands of test firings to discover the curve that produces what they want. The nucleation zone depends on firing temperature and glaze chemistry, testing is likewise required to discover it. Meticulous record keeping is critical to success; not surprisingly, many crystal glazes do it in an account at insight-live.com.

The evolution of the quality and aesthetics of your work, and even your ability to cut costs, are stunted when you depend too much on others (e.g. for firing, for premixed glazes). This mug is a good example of tests I need to do. This is G3933, made by adding iron oxide, rutile and tin oxide to a 75:25 blend of our base matte and glossy glazes (G2926B and G2934).
-It is crawling at some of the sharp angles of the incised decoration, would a little CMC gum fix this?
-Would an 80:20 blend of the two glazes give a little more matteness?
-Our red-burning body gives better color at cone 5, would this glaze be richer and more matte on it in the C5DHSC slow cool schedule?
-I want to test increases in the rutile (for variegation), iron (for better color) and granular manganese (for more speckle).
-Would a Ravenscrag Slip base glaze be a better host for the rutile, iron and tin?
Having a small test kiln puts all of these changes on my radar. An account at insight-live.com to document everything well brings it all together.

The challenge: Create a 3D printed case mold that incorporates a plaster section just for the finished surface.
Top right: The secret is M3 brass threaded inserts in pyramid-shaped 3D-printed anchors (I have just pressed them into the 4.4mm dia, 10mm deep, -3 degree tapered holes using a soldering iron). These brass/plaster pyramids embed into the plaster to provide a threaded hole that M3 bolts can screw into.
Upper left: We made a cross-section CAD drawing of a three-piece demonstration mold (upper left). The top plate has holes for the M3 bolts, air escape and natch clips and recesses for clamps to hold a 3D shell, with flanges, in place (not shown).
Lower left: The anchors have been screwed onto the upper plate.
Center left: The plaster was poured, and over-filled, then the top plate, with anchors, pressed down on top of it. After set, the plate was unscrewed and removed.
Bottom right: The plaster section has been reattached and natch inserts and anchors put in place. The plaster was not sanded or prepared, this is a demo.
What is this all about? A full master case mold, utilizing this technique, coming soon.

This is the most complex shape known that can fit together organically, without a pattern (dubbed the Einstein tile, it was discovered by mathematicians in 2023). It has six sides of 1 unit length, six of 1÷1.73205080757 and one side measuring twice the latter. Placing the tiles is tricky because it is only logical to seek a pattern, but there is none. One method is to start with a center tile and move outward in a spiral, being ready to backtrack and place them upside down when a piece cannot be fit. The tile shape is a product of connecting four identical irregular pentagons - each made by cutting a regular hexagon into three pieces. To achieve the maximum precision, 3D print multiple cookie cutters and let them stiffen and shrink in the cutters. To round the upper corners use stretch wrap) when stamping (print cutters in both orientations if doing this). Tiling a floor or wall will present issues with the number of edge tiles that need to be cut. However, cutting at least some custom edge shapes is practical because only 90 and 120 degree angles are needed.

Stoneware and porcelain plates having overhung rims and wide flat bases are extremely difficult to keep flat (as this potter discovered). In industry they are fired in setters, or even rim down, to temperature, then glazed and fired lower. As a potter, the best you can likely do is pay attention to the cross section shape (not too flared, inherently strong), fire on flat shelves, minimize changing shape on handling when soft or leather hard, dry evenly, avoid a sharp concave outer contour between foot and wall (bevel it well) and keep the center portion thick enough so it does not pull upward as the rims slump (especially if rims are thick). Working at low temperature can be a solution, but terra cotta clays are generally not stable for this shape if fired past cone 04. White burning low fire bodies are better but also more porous, so glazes must fit well to avoid crazing.