I wanted an easy way to make molds for slipcasting handles that mate perfectly to any shape mug (or pitcher, teapot, etc). I want to pair cast with thrown or jiggered elements and join them using just slip (even when the clay is stiff). We have developed a flexible CAD design that puts 3D printing of case molds within the reach of almost anyone. It requires so little tooling it can be done in a kitchen using spoon mixing and a paper cup! These PLA shells, for example, print quickly to only 11 grams and they peel away from the plaster with a heat gun to give fine detail and perfect fit. Multiple cycles of redesign and print are practical to achieve just the right shape and fit. Cast handles can be produced in quantity and stored in a damp box, removing one of the biggest hassles in the production of handled ware. The feel of the handle is the first thing customers notice, even a hobbyist can now turn a "wet noodle" handle into something designed and utilitarian. You can get this drawing on the downloads page. Worried about mixing or tuning your own casting slip recipe? See the link at the bottom of the source page for this post.

This is L4023F (a test body like our H440 cone 10R body). The polygons on this surface are produced when the 3D CAD software converts from its native format to an STL file that slicer software can use. These are the product of the default settings (which can be changed but increase file size). The precision of the 3D printer is evident in that it can reproduce these. Since the polygons are not visible in the final glazed piece, neither the PLA surface on the 3D printed block mold, or the surface of the plaster case mold made from it, were sanded.

Feldspars are employed in glaze recipes as melters. So comparing their melt fluidities should be helpful in deciding if one can substitute for another (of course, if possible a soda predominant feldspar should be substituted for another soda spar). Feldspars don't melt alone at cone 6 (2200F) so we mixed each with 15% Ferro Frit 3195. Nepheline Syenite is obviously the champion melter here. Other similar ones can be spotted easily. In the end, degree of melt is a valid consideration in determining if one feldspar is a viable substitute for another in a recipe. Even if the feldspar you want to substitute does not melt as much a little frit can be added to the recipe to make up for the difference (e.g. 3-5%).

Only three tile shapes were needed. The fish cutters were 3D printed to both cut and stamp at the same time. Multiple slightly different sizes of the triangle and trapezoid were made to accommodate irregularities and keep joints tighter. The clay is M340 and the glazes are Amaco Celadons and Potter's Choice (for brushing). These are small and we found that a good way to paint them was to glue them down to a plaster slab with a few drops of glaze (it was easy to scrape off when the three coats had dried).

This glaze is "stretched" on the clay so it cracks. When the lines are close together like this it is more serious. If the effect is intended, it is called "crackle" (but no one should intend this on functional ware). Potters, hobbyists and artists invariably bump into this issue whether using commercial glazes or making their own.

"Art language" solutions don't work, at least some technical words are needed to understand it. Crazing is a mismatch in the thermal expansions of glaze and body. Most ceramics expand slightly on heating and contract on cooling. The amount of change is very small, but ceramics are brittle and glazes are rigidly attached. If they are stretched on the ware cracks will occur to relieve the stress (usually during cooling in the firing but sometimes much later). All glaze manufacturers advise against crazing on functional ware.

In 2025 ChatGPT’s four glaze adjustment suggestions are either wrong or will accidentally fix crazing because they address other issues that just happen to also be present. Adding enough silica or alumina brings unacceptable side effects on multiple fronts. Alkali fluxes need to be substituted, not reduced. Simply substituting frits changes the overall chemistry making it a different glaze - why not just use a recommended recipe for the body as suggested by Gemini? Adding silica to a body increases, not decreases, the thermal expansion (and it reduces vitrification). Increased vitrification doesn’t make the body resist crazing (bodies don’t craze) - unless increased vitrification happens to also increase the thermal expansion (but not introduce warping). Slower cooling or a lower refire only delays crazing. Comparing COE’s of body and glaze is impossible for anyone not having a dilatometer to test both (you cannot compare measured and calculated COEs and calculation of COE for bodies is impossible). Embracing the crazing is a no-go for functional ware.

Gemini correctly explains why it happens. But, it suffers similar misconceptions about vitrification, cooling, silica additions to the body, vitrification and ignores the side effects of increasing silica or alumina in a glaze recipe. It is right that alkalis need reduction, but fails to note what to substitute. It recommends zinc as a stabilizer (whatever that means), but zinc is a strong flux that should be substituted for KNaO. Thinner glaze coating just delays crazing. Its suggestions about experimenting, keeping records, and researching to find recipes known to be compatible with the body are good. The only information available from glaze or body suppliers that might help is a chart that permits ordering products from lowest to highest COE (enabling you to at least transition in the right direction for better fit).

We wanted to compare the melt fluidity of G2934Y (left) to G2934 (right). To do that we prepared GBMF test balls (see below). The forming and drying process leave a flat spot so the gumball-sized balls are easy to place on a porcelain tile. During firing they flatten out. The degree to which they do acts as a measure of the flow (when compared with another). Many characteristics that one would not observe on glaze tiles reveal themselves in this test. In this case, we needed to know if the melt flow was at least as good (and this proves it is better). Reactive glaze tend to be the norm in recent years, their primary characteristic is being runny (having high melt fluidity). Their fired character...

Reactive glazes don't melt into a homogeneous melt and they don't freeze as a typical glass. The physical nature of the material powders (e.g. their particle size and the individual nature of how they respond to heat, soften, melt and interact with their own kind and others) create a melt that does not solidify into a homogeneous glass. These glazes are said to be dynamic. And unpredictable effects often occur during firing, like color variegation, speckles, streaks, mottled and flowing textures, crystallization, pooling, etc. The outcome is influenced by factors such as the materials chosen to source the needed oxides, firing schedule, kiln atmosphere, cooling or heating cycle, etc. These glazes are at their best when each piece has a unique, artistic character. But, this is also their worst feature, making them "tipping point glazes", ones whose visual character is a product of fragile and not well understood features of the materials and process. Small changes typically produce big changes in fired appearance (often to the chagrin of the potter).

For many years we have searched for a credible alternative to our Lightnin lab mixer. We found this unit on Amazon but then bought it from FristadenLab in Nevada. These are made in China but packaged, documented, shipped and supported in Nevada. This cost about $300US (a programmable one costs a little more but this is the better option for ceramic slurries). The first impression is how heavy the unit is. The base is 1/4" solid steel. The rods are all solid stainless 5/8". The clamp is also solid metal. The shaft is 3/8" and is held in place by a good quality chuck which enables easy release. The propeller is about 2 1/2" in diameter and screws on, it would thus be easy to 3D print other propellers and mount them on a hex nut (e.g. to fit into glaze jars). The locking mechanism enables mounting at an angle (important when trying to achieve the highest speed without sucking air bubbles). It plugs in via a 24v DC adapter (which means it has a DC motor). When switched on it speeds up gradually and the dial offers fine control of speed. On this occasion, we mixed 3500g of plaster in this 2 IMP gallon bucket (2.5 US gallon) with no problem. It runs completely silent and should easily mix this pail full of glaze or casting slip. A propeller mix like this is a great start to DIY glazes.

The way potters and hobbyists traditionally pack electric kilns is the height of energy wastage. This 18x22 hexagonal kiln load of bowls is a good example. A traditional pack on the left does 24. The new method using 3D printed setters on the right does 36. The left firing contains only 5.3 kg of bowls with more than 60kg of furniture - each 220g bowl incurs 2700g (6 lb) of kiln furniture weight - seven times as much! This type of packing also leads to uneven firing and puts a heavy load on the electrical components. The bigger the kiln the greater the efficiency.

These light-weight stackable setters don't exist yet. But they soon will. I designed specifically for this bowl and printed samples using PLA. Sintered alumina, the ultimate material, has 3x density over PLA - so we can predict the weight at 160g. These setters allow free flow of air, even the foot of the bowl is exposed. They can be printed upside down with one pass of the nozzle for most of the geometry.

New uV hardened resins for dental applications are the inspiration for this idea. These resins and hardeners are commodity items online now, anyone with a clay 3D printer (or the ability to retrofit an existing PLA printer) can experiment with recipes (even of inexpensive refractory materials like kaolin, ball clay silica) and print these.