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Paint another layer onto a fired glaze? Yes. With CMC gum.

The cone 6 mug on the left has the G3933A glaze, applied as a dipping glaze. It turned out poorly - crawling from corners and looking thin and washed out. I made a brushing glaze version of this (which adds 1.5% CMC gum), I keep it around for this very purpose. It has a high specific gravity (unlike commercial ones that have high water contents - they will run and go on too thin if you try this). Because of the gum it dries hard, there is no shrinkage or cracking. On a second firing, using the C6DHSC schedule again, (mug on the right) the surface is transformed - thicker, more vibrant color (being picked up from the underlying body).

Context: CMC Gum, Six layers 85 Alberta.., Control gel using Veegum.., Convert a pint of..

Wednesday 28th February 2024

Finished cast v1 stoneware beer bottles

Cast ceramic beer bottles

The center bottle is a standard glass one, the other two are ceramic, cast out of the version 1 plaster mold. The stopper fits perfectly. The clay is Plainsman M370 + 10% raw umber, it fires black. The glaze is GA6-B. They were fired using the C6DHSC firing schedule. The slightly larger size will enable inserts at the bases to inlay a logo or other info. These bottles are a testament to how 3D printing and 3D design now make it possible for even casual potters to make pieces never before practical or even possible.

Context: First slip cast leather-hard.., Version 2 beer bottle.., Beer Bottle Master Mold..

Saturday 24th February 2024

Version 2 beer bottle mold - done right this time

Casting a rubber case mold for the beer bottle

This time I printed the case mold, rather than the block mold, in six pieces on my consumer 3D printer.
Top: I printed the two halves upright. Because the print lines run concentric the quality is so much better than the previous version printed flat. The ribbing inside made the halves strong so they did not go out of shape when filled with plaster (to give them weight).
Second: The mold halves were simply laid against each other - they mated perfectly. The four shells were then clamped in place.
Third: The PLA was soaped (using Murphy's Oil Soap) and rubber poured in (Smooth-On PMC-746). The next day it easily pulled out.
Fourth: The finished rubber block mold. The sides are pretty flabby so I made them rigid for casting the plaster working mold using the four shell pieces (placed upside down). Shown right is a bottle made from the version 1 mold - this mold will fix its issues (slow extraction time, poor surface),

Context: Finished cast v1 stoneware.., Beer Bottle Master Mold..

Saturday 24th February 2024

AI can create impossible designs for pottery.

A strange AI porcelain mug

Consider these porcelain mugs I made at At first, they look pretty typical but take a closer look at the one in the middle. The floral design on the one behind morphs into the actual 3D shape on the one in front. I seriously want to make a mug like this! Imagine the ideas you could get using AI tools (no wonder #aiart is such a big deal). Of course, there are lots of ethical issues and climate impact.

Context: These pots never existed..

Saturday 24th February 2024

These pots never existed. How is that possible?

AI generated pottery

I created these images using the "imagine" command at This is jaw-dropping, at least for me. For the top left one I asked for "stoneware pottery mugs with floral decoration covered by a glossy transparent glaze". For the vase I specified "crazed transparent glaze over floral decoration". Notice that for the porcelain mugs I forgot to specify "hand made", that mugs only have one handle and that decoration should only be on the outsides but not on the handle (an indication to me that this AI is genuine). For the last one, I asked for a piece demonstrating the difference in runniness of two different glazes. How does it know what crazing and runny glazes are? How does it know a bowl would be the best shape to demonstrate the latter? How can it even be that AI is turning out to be best in the liberal arts? Ethical questions also abound here. Apart from the obvious consider the question about environmental impact. AI requires computing power akin to what bitcoin mining took. And an unstoppable AI tidal wave is going mainstream. nVidia could become the world's largest company. The potential for impact on our planet is far beyond just worrying. Consider the impact on our ability to trust: If we cannot even trust pottery to be real what can we trust?

Context: AI can create impossible..

Saturday 24th February 2024

Drying cracks in bricks - why is this happening?

Bricks cracking during drying

These bricks are being extruded in India and the plant is suffering drying cracks. A consultant recommended the addition of lignosulphonate (at a cost of $800/ton) as a solution. But before adding such a large expense, some obvious changes seemed in order first. The technician knew the plasticity index of the clay (a measurement used for soils) but he did not have records of its drying shrinkage, water permeability, drying strength or drying performance. When problems like this arise the value of such becomes evident - that knowledge provides direction when things like this happen. It would answer some questions. Is cracking happening because of lack of drying strength or plasticity or because drying shrinkage is too high. The splitting along the corner of the extrusion is a clue that plasticity could be lacking - that could be solved by a small bentonite addition or reduction in grog. If permeability is low an increase in grog might be needed (if the pugmill can extrude slugs with a smooth edge and corner). Notice the cracks that start from those splits (lower left). But also notice how the top edge has shrunk while the center section has not. That indicates a drying process that is not engineered to subject all surfaces to equal airflow (sure enough, these are being dried outside in the sun and wind). Another factor is cross-section: The round holes create variations in thickness that exceed 300%, square holes with round corners would be better. Given the location and economic realities, the change to square holes might be enough to ignore all the other issues and get away with it.

Context: Bricks and tiles are.., Clay lab report Is.., Physical Testing, Cracking of Clays During..

Friday 23rd February 2024

The incredible plasticity of bentonite. It is the secret to win the ThrowDown!

Two dissected vases showing the comparison in wall thickness

The 20cm vase on the left is thrown from what I thought was a very plastic body, M370. I achieved close to the same thickness top-to-bottom (5mm). The one on the right was the same original height, 20cm. But it has dried down to only 18cm high, it shrinks 14% (vs. 6% for the other). The thinnest part of the wall is near the bottom, only 2mm thick! How is it possible to throw that thin? The body is 50% ball clay and 50% bentonite. Bentonite, by itself, cannot be mixed with water, but dry-blended with fine-particled ball clay it can. That bentonite is what produces this magic plasticity. But it comes at a cost. It took about four days to dewater the slurry on our plaster table. And one month under cloth and plastic to dry it without cracks.

Context: Bentonite, Drying Ceramics Without Cracks.., Plasticity

Friday 23rd February 2024

Coarse body fires with smoother glaze

Glaze fires better on coarse body

On the left is Plainsman M332, a sandy and coarse body dry ground at 42 mesh. On the right on a wet-processed body, sieved at 80 mesh and then filter pressed - it is porcelain smooth. Yet that glaze, GA6-C, on the smooth body is covered with blister remnants while the same glaze on the coarse body is glassy smooth (they were in the same firing). That smooth glaze is courtesy of the C6DHSC slow cool firing schedule. But why does it perform so poorly on the finer body? That body is being overfired. Pieces are warping. Although not bloating, it is beginning to decompose and generate gases, they are producing the blisters.

Context: Melt flow test demonstrates.., Glaze Blisters

Tuesday 20th February 2024

Same glaze on black stoneware and white porcelain

The same glaze on black stoneware and porcelain

The glaze is G3948A iron red fired at cone 6 using the C6DHSC schedule. The bodies are Plainsman Coffee Clay and Polar Ice (the insides are different glazes). They were in the same kiln. These mugs demonstrate how much reactive glazes can interact with the body beneath and how much that affects their fired properties, especially when they have high melt fluidity like this one. On the left the glaze is drawing color out of the body. The porcelain on the right has no color to give but it does have sodium - and it is supplying enough to act as a catalyst to the creation of the iron crystals.

Context: Melt flow test demonstrates.., Iron red glaze fired.., Reactive Glazes

Sunday 18th February 2024

How I got a better matte black: Cone 5 instead of 6

Three matte black pottery mugs

In our electric kilns, cone 5 finishes at 2163F (vs cone 6 at 2200F). The bodies I normally use need cone 6 to vitrify to the degree I want. But not so with our MNP, it is vitreous at cone 5. And our black matte G2934BL glaze just happens to produce better matteness at cone 5, especially with the cone 5 C5DHSC firing schedule. The inside glaze is L3500G, it is melting just as well as at cone 6.

Context: Cone 5

Wednesday 14th February 2024

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