Dipping glazes peel like this because they contain clay and shrink as they dry (the fact that all of them don't do this is actually amazing). Success is a matter of the shrinkage being low enough, the drying being fast enough, the layer being thin enough, the bisque being absorbent enough, and the bond with the bisque being good enough. Glazes with high clay content, thick applications or multi-layering are the main offenders. Thixotropic slurries apply most evenly and are least likely to go on too thick. Dipping glazes having 15-20% kaolin or ball clay are easiest to slurry up and have the best application and drying properties. Mixing base layers as first-coat dipping glazes is also important.

The problem with this piece: The addition of 7.5% bentonite to make up for the otherwise low raw clay content in the recipe produced a recipe that does not pass a sanity check. When that was replaced with kaolin it worked. There is a crowbar approach to fix these without any other changes: Add CMC gum (e.g. 1%) to make them brushing glazes.

G1214Z1 is a popular cone 6 calcium matte glaze recipe. It has very high melt fluidity, enabling a fine grained crystalline matte surface to develop during cooling. A potter was steered to this recipe after finding that G2934 magnesia matte fired too variegated when stained blue. However, her first effort with this failed a leaching test. She had a secret weapon: An account at Insight-live.com, where recipes and their calculated oxide formulas can be compared side-by-side. Leaching glazes are most often runny because they contain excessive fluxing oxides. She simply increased the SiO2, it is the glass that makes up the lion's share of all glazes (higher amounts of it characterize glossy glazes). Al2O3 couples with it to improve durability (and the Si:Al ratio is a factor in the degree of matteness). With an accompanying small increase in the B2O3, the magic glass:flux that makes most cone 6 glazes possible, the got the result on the right. The good news: It passed the GLLE test for leaching. There is a lesson here: She had to compromise the degree of matteness a little to get the food safe product. A benefit is that it is also less prone to cutlery marking. Happily, it turned out that much less blue stain was needed.

Dolomite is a key material for glazes, especially mattes. We were forced to adopt a new brand and needed confidence it was equivalent. Three tests were done to compare the old long-time-use material (IMASCO Sirdar) with a new one (LHoist Dolowhite). The first melt flow tester compares them in a very high dolomite cone 6 recipe formulated for this purpose; the new material runs just slightly more. The second tester is uses the G2934 cone 6 MgO matte recipe with 5% black stain; the new material runs a little less here. The third test is the high dolomite glaze on a dark burning clay to see the translucency and compare the surface character. They are very close. These three gave us the confidence to proceed.

These two Plainsman M370 test mugs were fired at cone 6, the left one with G2934 matte glaze, the right one with G2934Y4 matte. They look and feel identical in the hand. The two glazes have the same chemistry. But they employ different materials to source that chemistry. The secret of of the matteness is high MgO (magnesia content). In the glaze on the left MgO is sourced by dolomite, a lot of it. The glaze on the right sources it from a special frit, Ferro 3249. The impact of this difference is visible in the melt fluidity tester, the fritted one is melting and flowing much better. On other clays, especially stonewares, the G2934 can have a dry surface that cutlery marks. Thicker applications make it worse. But the Y version exhibits no such issues. Its mattness, durability, cleanability and hardness are so good that it is being used in floor tile.

These cone 6 glazes are the same (G3806G), except the one on the right has 3.5% copper carbonate added. Copper is commonly fluxes glazes, making them melt more. But in this case it is not, the clear base is running just as much as the stained one. Either the percentage is not high enough or the host transparent glaze is resistant. Another observation: I was suspicious that the micro-bubbles in the glass matrix were coming from the copper carbonate gassing during firing. But not so, as you can see on this melt fluidity tester, the flow on the left has many more (it appears less melted because of this). In this specific glaze it seems probable that the copper bubbles (generated as it decomposes) act as a fining agent to coagulate and help clear the others.

Here is why the stair-casing artifacts are not the problem many people think. These are stonewares fired at cone 6 oxidation. The dark one is M370C with 10% added raw umber. The other is M370C. Both are glazed using GA6-B Alberta Slip amber transparent. The wood-grain texture on the right is an artifact of 3D-printing - the case mold was printed flat rather than upright. Strangely, that is the bottle people want! But the production prototype bottle is the one on the left and the stair casing is barely visible. Additionally, these are prototypes, the production molds would either be made by printing the model upright or by casting a plaster model of a bottle half, smoothing and soaping it, attaching it to a clamping baseplate and then setting up 3D printed railing around it.

Same clay body: Plainsman Coffee Clay. Same glaze: MA6-C rutile blue. But the mug on the left was fired in the PLC6DS schedule (normally that one does not produce this much blue, but the heavily pigmented clay brings it out). The one on the right was fired in the C6DHSC schedule. That schedule also improves the gloss and surface quality of the inside GA6-B liner glaze.

3D printing is resetting and revolutionizing all fabrication industries. It has taken hold because it brings exciting new capabilities we never had before, especially in ceramics. Each disadvantage is being addressed and solved. This stair-casing, or more correctly, "printing artifacts", are often cited as a reason not to adopt 3D. But these are not an issue here. First, most of the surface on this case mold is not exposed on the final piece. Second, near vertical and fully horizontal printed surfaces, such as the shell around the outside and the spacer ring, don't have artifacts. Third, this bowl model is not 3D printed, it is plaster that was poured into a 3D printed shell. Before use, this will be stuck down onto a potter's wheel and tooled smooth. It is then attached to a clamping baseplate and the 3D printed railing clamped around it.

It is a clay, a very non-plastic one. These are fired SHAB test bars of Barnard Slip going from cone 04 (bottom) to cone 6 (top, where it is melting). Porosity is under 3% and the fired shrinkage above 15% from cone 1 upward (second from bottom). Drying shrinkage is 4% at 25% water (it is very non-plastic). The darkness of the fired color suggests higher MnO than our published chemistry shows (and also higher iron). The white areas on the lower temperature bars are soluble salts.

Since this is a fine particled material, it could likely be made plastic with a bentonite addition, likely 5% or more would be needed. Solubles could be precipitated using barium carbonate.

Long after installation, handmade clay tiles can be susceptible to chipping at the corners and edges. This is more of an issue when the tile is glazed. As the temperature of the tile increases from the heat of the sun, the dimensions increase and they can begin to press upon each other. This can create high compressive stresses at the bearing points. If the gap between the tiles is not sufficient, the stress at the bearing point can continue to build until a piece cracks out of the corner like this. Terracotta tiles are most susceptible because they have much lower strength than vitrified ones. Since such handmade tiles have been in use since ancient times makers have always needed to compensate for this issue.

Of course the installers of the tile bear the main burden of avoiding this problem. However, in the manufacture of the tile itself, various things can be done to minimize the issue. For example, if an engobe is used, pay attention to its compatibility to the body (e.g. it needs a similar firing shrinkage and thermal expansion). Likewise with glazes, they should fit (not be under excessive compression or tension). Rounded corners are better than angular ones. Another option is to fire the tile to a higher temperature to get more strength - with caution since this can significantly increase firing shrinkage.