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It takes 80 pallets of dry materials to make a run of 4000 boxes of M370

M370 is now our second-most-popular clay body. Are you curious of the recipe? It is really quite simple. It has enough silica to resist crazing. It has enough Nepheline Syenite to mature to 1% porosity at cone 6. The rest is a mix of #6Tile kaolin and M23 ball clay with a little added bentonite to push up plasticity.

Friday 14th June 2019

G3806C with lower thermal expansion

G3806C has been our recommended base recipe for reactive glazes (by the addition of colorants and opacifiers). It excels for copper blues, for example. But its thermal expansion is high enough that it crazes on some bodies (e.g. Plainsman P300). To adjust it (via glaze chemistry) I introduced some low expansion Li2O (from Spodumene) at the expense of high expansion KNaO, this dropped the calculated COE from 7.1 to 6.6. The melt fluidity, shown here at cone 6 (its most important feature), is exactly the same. The color is bluer. But not as dark, so copper oxide might be better. Or a higher percentage of copper carbonate. The base recipe (without the copper and tin) is potentially very valuable to create other reactive effects that depend on melt mobility. Why? Because it is very difficult to create a high gloss melt fluid glaze that also has a low thermal expansion.

Monday 10th June 2019

Supercharge the plasticity of cone 6 reclaimed clay

If your reclaim is short and non-plastic you can make it better-than-new by using an additive of 50% ball clay and 50% bentonite. While only a few percent bentonite supercharges the plasticity of any clay body it is almost impossible to get it to mix into a wet slurry or plastic clay. But thoroughly shaking it together with ball clay (in a plastic bag) separates the super-tiny particles of bentonite between the almost-as-tiny particles of ball clay, that new powder will easily mix with water. And it fires to a tan-buff stoneware at cone 6 so it won't change the fired appearance of most buff or brown cone 6 stoneware bodies.

Friday 7th June 2019

It is impossible to dry this clay. Yet I did it. How?

These are made from a 50:50 mix of bentonite and ball clay! The drying shrinkage is 14%, more than double that of normal pottery clay. It should be impossible to dry them, the most bentonite bodies can normally tolerate is 5%. Yet notice that the handle joins with the walls are flawless, not even a hairline crack (but the base has cracked a little). Remember that the better the mixing and wedging, the smaller the piece, the thinner the walls, the better the joins, the more even the water content is throughout the piece during the entire drying cycle and the more damp of a climate you live in the better your drying success will be. What did it take to dry these: 1 month under cloth and plastic! I changed the cloth every couple of days. So by implementing these same principles you will have better drying success.

Tuesday 28th May 2019

Brushing glazes can go on unevenly for more than one reason

Both of these were glazed by brushing. The inside transparent and white glazes are fairly easy to apply evenly but the bright color on the outside left one certainly is not. The problem is a combination of things. It is difficult to apply it evenly with a brush. It is difficult to get it on thick enough. And this commercial glaze does not contain enough of the purple stain (so I added 6 grams of Mason 6304 Violet stain powder to the 2/3 of a jar I had left, and mixed thoroughly). That, more careful brushing, and an extra layer produced the piece on the right!

Tuesday 28th May 2019

Partially and fully opacified cone 6 G1214Z matte glaze

This is a calcium matte base (as opposed to the magnesia matte G2934). The clay is Plainsman M390. 5% Zircopax was added on the left (normally 10% or more is needed to get full opacity, the partially opaque effect highlight contours well). 5% tin oxide was added to the one on the right (tin is a more effective, albeit expensive opacifier in oxidation). The PLC6DS firing schedule was used.

Tuesday 28th May 2019

Body made from Plainsman Fire-Red, ball clay and feldspar

Fire-Red is an unusual material for several reasons. It has a high iron content yet is a fireclay (the iron percentage is so high that it fires black at cone 10R). It is also non-plastic. Most important, it is not ground to 200 mesh like industrial materials. This body demonstrates it well: 42.5% Fire-Red, 42.5% ball clay and 15% feldspar. All that ball clay gives it awesome plasticity. The feldspar gives control of the degree of vitrification (just raise or lower it for more or less). This recipe produces good density and strength yet still exhibits deep red color! Look closely at the surface: It is covered by thousands of tiny iron eruptions, these will bleed through an over glaze to give "speck-city" like no other!

Monday 13th May 2019

Want bright orange on your ware?

Orange is a very difficult color in ceramics. Inclusion stains are the only reliable method and universally used in industry. But you could ignore that and try a bunch of recipes online, buying exotic materials to complete each one. Maybe one will be orange enough, but will it craze or run or blister or leach or cutlery mark or crawl? Or you could put an orange stain into a transparent glaze you already know works on your clay. Or, how about trying a premixed orange at low fire? Ware can be amazingly functional and there are so many other bright colours available.

Friday 10th May 2019

When the cone does this I need to adjust the program

This is a cone 04. It is bent too much, the kiln has over-fired a little (cone 03 was also bent somewhat). The built-in firing schedule goes to 1945, that would be much more over-fired than this was (and the built-in ones do not soak, drop-and-soak or slow cool). It only takes a minute to edit the program I made, all I have done is drop the step-three temperature to 1930 (it was 1935). I adjust my schedule fire-up-to temperature as needed, I cannot imagine not doing this.

Friday 10th May 2019

Soda fired porcelain vessel by Heather Lepp

This is a small cup-sized object made from Plainsman P600 (simply composed of Tile #6 kaolin, nepheline syenite and quartz). It is valued as a product-of-the-process piece, consigned to the "kiln God" as unglazed. It exhibits carbon-trap, soda glaze deposition and flashing. The soda-vapour atmosphere of the kiln glazed one side of the vessel early enough in the firing to trap carbon under a crystal-clear glass. Often such glazes are crazed, but this one likely is not because the body contains 25% quartz, giving it a high thermal expansion. The other side of the piece exhibits tones of red, brown and yellow on the bare, vitreous porcelain surface - this is characteristic of "flashing".

Friday 10th May 2019

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