This plate, by Pablo Picasso, is on display in the art gallery on our Princess cruise ship. While others notice the underglaze designs, and the $40,000 price, I notice the absolutely crystal clear and bubble free transparent over glaze. How did he do that? At the Madoura studio they used leaded glaze. Most potters using borosilicate glazes would envy this. Any hope of even approaching the quality of a leaded glaze is keeping temperatures at or below cone 06, a thin glaze application, a low carbon body and ceramic stains rather than metal oxide colors.

By Picasso’s time, European low-fire traditions already had a well-matched clay/glaze system. Glazes were lead bisilicate frit with enough kaolin or ball clay (e.g. 10%) to suspend the slurry and enough silica (likely 20–30%) to bring the COE down within reach of the body. They didn’t use talc in the body, rather it would have contained 50-70% ball clay/kaolin, some feldspar as a filler (since it does not flux at low fire) and enough quartz to raise the thermal expansion within the range of the glaze.

This is a reactive pottery glaze, Jen’s Juicy Fruit. It runs. And crystallizes. That can look great on a test tile but for food surfaces there are strings attached. Behind the magic a tangle of headaches can be lurking: Leaching, crazing, poor durability. And even expense (this kind of melt fluidity usually requires wallet-busting lithium). But hey, why not go for it! Stuff it with metal oxides and get some real sparkle brewing. Then push it even harder, with slow cooling, for those big crystals. Congrats, now you’re brewing a science project. And flirting with leaching and toxicity. And there is more. These effects most often depend on high sodium or potassium (aka high feldspar), that’s a recipe for off-the-charts thermal expansion - and thus crazing. Is this glaze something you would want on a food surface? Suddenly that “wow” glaze starts to look… not so wow.

Hey, why not just fix it? Reduce that high KNaO, increase the SiO2 and Al2O3. Congrats. Now it looks totally different. And boring! With these types of glazes it is common that no matter what you do, you cannot maintain the character while fixing the problem. Why? The visual character depends on the problems! So use this. But not on functional ware.

Rick doesn’t dig clay, crush rocks, or make glazes. Ew, messy. He buys commercial glazes in cute little jars, each the price of a steak dinner. Sure, back in the dark ages, potters used actual dirt and rocks. And, around here you can even get a ton of gravel or clay, for $20. But today, potters shell out twice that for one box and say, “Totally worth it!” OK, fine. But glaze is where it gets magical. A ton of local gravel is packed with feldspar, silica, calcium carbonate, dolomite — a whole cone-10 party (that can be moved to a cone 6 neighborhood with a little frit). Grind it, add clay, dip, done. How is it possible that an overloaded pickup truck full costs half the price of a single 500ml jar Rick uses? Something’s upside down here! Rick says: “Why mess with base recipes or spend all that effort learning and testing DIY dipping glazes when I can spend minutes multi-layering these commercial paints”! Of course, he has to brush up the price to pay for them! And sure, some customers might question how glazes that have such intense metallic colors and run like mascara in the rain are not silica-starved metal-oxide sludge. Rick answers: “They have safety labels, with fancy symbols, so I don’t have to think about that”. The icing on the cake it how well they photograph and how good they look on Rick’s social. He really has this thing figured out. Tradition is overrated anyway, right?

This recipe, G2826A, a base transparent recipe having 50% Gerstley Borate plus 20% kaolin, is "jelly city". Although a low temperature base, this was much more commonly used at cone 5-6. This recipe, G2826A, was at the limit of how melt fluid a glaze could be. And at the limit of the slurry properties that could be tolerated with this material. In this test, even with 2.5g of Darvan deflocculant in this jar, it was still thick enough to require pushing this tile down into it! It still needed 5 seconds to build up enough thickness. And did not cover the recesses properly. Yet people have used this popular fluid-melt recipe for 50+ years to get the surface variegation it produces (because of boron blue) and the fluid melt (because it is so high in boron). They added all manner of colorants and opacifiers and it generally performed without blistering. The melt fluidity required careful control of thickness (to avoid it running onto shelves). This was a "Dr. Jekyll and Mr. Hyde" of ceramic materials!

Potters are using Gillespie Borate in this recipe (with issues), see the G2826A2 recipe. Other approaches are to source the boron (B2O3) from a frit (or mix of frits). An example is G2826A1, it does not variegate as much but added titanium or rutile can emulate that. Another hybrid option is the G2826A3 that employs both Gillespie Borate, nepheline and talc.

Left: 65% #6Tile kaolin and 35% nepheline syenite. Although it has great plasticity and fires white, it crazes the glaze and has 1% fired porosity (using the SHAB test).
Right: 65% M23 Old Hickory ball clay (similar to OM#4) and 35% nepheline syenite (feldspar would also work). The glaze fits, the body fires very dense (zero porosity) and plasticity is fantastic!
The body on the left needs a 20% silica addition (to stop the crazing) and more nepheline (to reduce porosity to porcelain levels). The remaining 40% kaolin will not be nearly enough for a workable plasticity (so bentonite will be needed). The body on the right does not need fixing; it works as is. Many feel that stoneware body recipes must be built on a feldspar-containing base clay having pottery plasticity (adding ball clay, kaolin, feldspar and silica and ending up with needlessly complicated recipes). But, ball clay is a base, all it needs is a non-plastic filler (to cut plasticity and therefore drying shrinkage) and a flux to vitrify it - feldspar or nepheline fills both roles.

Of course, this stoneware does not fire as white. But do you need white? Glazes will fire brightly colored on this surface. And, cleaner ball clays are available in many areas (even ball clays intended for casting will be plastic enough). It is also worth considering the use of a white engobe.

Until now, I have done these in Fusion 360. But in OnShape and my new dimensioning method they are even better. If you are a hobby maker like me, then OnShape is free. This updated design only has three parameters: ID (inside diameter), OD (outside diameter), and slack (addition or subtraction for a good fit).

Print all four of these at the same time. Repeat cycles of adjusting the slack parameter and printing again until they fit into and over each other well (the better quality your printer to smaller the "slack" dimension can be). Print them in multiples of seven: Two natches, two embeds, two clips and one spacer (these are the proportions in which you will be consuming them).

An advantage of OnShape is that it enables sharing; the link is below. To 3D-print it select all four, right-click on one of them, export to 3MF format, open that file in your slicer software, position (and replicate/orient items), then print or export to a G-Code file.

I am just a simple guy, a hobby 3D printing "Maker", I focus on making molds for ceramic slip casting. I don't need a "high maintenance" CAD partner.

Fusion 360 and I were not a good match. It was her world, Windows and Mac only - I had to live in it. She was the “Queen of Complicated”, always on the drama channel of new features far beyond what I needed, rather than refining the simple ones I did need. And she was expensive to take out, costing way more than what I needed ($750/year).

OnShape is my new chill. She will go out, at full power, to Linux and iPad. She's a keeper. I don’t need a user manual for her. She's not a princess but a partner, social not a snob. I don't feel like I am on a roller coaster without a seatbelt, rather I am with someone that is easy to be around and way more powerful than she looks.

This 3D-printed PLA pour spout potentially increases the utility of this one-piece plaster mold. As can be seen on the upper section analysis, the spout is designed to form the lip of this small Medalta Potteries bowl (and provide a guide for cutting its inside edge). It has lugs that extend outward to enable holding it down using rubber bands. I intend that it will be cleanly removable after the piece begins to pull away from the mold, leaving a high-quality lip that only needs a little trimming. This spout also permits precise monitoring of when to pour out the slip and it prevents most of the mess made using traditional molds having a spare.

This is the first piece I have made wholly using OnShape CAD. Experience with Fusion 360 gives me expectations of how this should work and those expectations are generally being met. Cost is no longer an obstacle to adopting professional 3D CAD for mold making. I am using OnShape on my 2014 Mac Mini running Ubuntu Linux (on 16gb RAM). And Prusa Slicer, OctoPrint, GIMP, Kdenlive, InkScape and productivity software are all running smoothly on it.

These (right) were made individually in the factory during the 1930s and 1940s (the insides have pronounced throwing rings and slip drips). The potters were able to make up to 500 per day, even though they took the time to smooth the outside using a rib! The inside base of this one is bowl-shaped (the walls near the base are very thick), this helps explain how they were able to throw them so quickly.

Perhaps most surprising is how much whiter and speck-free the bottle is even though it is fired four cones higher than the crock (Plainsman M340 at cone 6). Both pieces have porosities above 2%. Why? First, they got their clay from further east in Saskatchewan (near Willows), where the cleanest clays are much lower in iron contamination (likely the H0009 body). The whiteness is better even though they would have had to add some ball clay to make the clays more wheel-throwable. Second, they employed a wet process to refine the clay (slaking, blunging, sieving and filter pressing), this enabled them to sieve out the iron pyrite particles. Fortunately, modern dry grinding and air separation equipment is greener and able to accomplish without water.

Notice also the transparent G1129 glaze on the beer bottle (the upper section is likely the same glaze stained using iron oxide): After almost 100 years it has not crazed. This is both a testament to the ease of glaze fit these natural materials offer (because of the high quartz content) and the skill of the engineers of the time at matching the thermal expansion of glaze and body.

The original bottles were hand thrown and very heavy. This one, for example, weighs 525g. Our bigger slip cast equivalent with a modern shape, 3mm thick walls and much higher capacity weighs only 400g.

The color, enduring glaze fit and the type of clay used by Medalta indicates these were likely fired at least to cone 10. Energy was cheap at the time and the Saskatchewan clays they used require high firing.

This is a test mold to determine if the swing top stopper will work on a neck of this shape. This mold only weighs 87g and the walls are printed to only 0.8mm thickness. Two natches are sufficient to keep the halves aligned perfectly. Pieces will shrink about 12%, thus the larger size. We will use tissue transfers for the decorations, the GA6-B glaze for the inside and shoulder and G2926B transparent for the body.