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This is how much casting slip 10,000 grams of powder makes

To-the-brim the bucket holds 8.8 liters (2.43 Canadian gal, 1.9 US gal). The slip itself weighs 14 kg (30 lb). It has a specific gravity of between 1.75 and 1.8. The slurry was power-mixed in a larger bucket.

Friday 22nd November 2019

Is the clay too stiff to use? Maybe not.

Clays of very high plasticity often stiffen during storage in the bag. This is Plainsman Polar Ice, it contains 4% VeeGum. This slug is like a brick, yet it will loosen up completely. But it is far too stiff to attempt wedging. However simply throwing it on the floor a few times (turning it each ... more

Thursday 21st November 2019

Serious blistering at low fire: How to fix it

An extreme example of blistering in a piece fired at cone 03. The glaze is Ferro Frits 3195 and 3110 with 15% ball clay applied to a bisque piece. Is LOI the issue? No, this glaze has a low LOI. Low bisque? No, it was bisqued at cone 04. Thick glaze layer? Yes, partly. Holding the firing longer at ... more

Wednesday 20th November 2019

Deep, deep blue without any cobalt. How?

These have to be seen to be believed, it is the deepest, richest blue we have ever produced. This is Plainsman M340 fired to cone 6. Black-firing L3954B engobe (having 10% Burnt (not raw) Umber instead of the normal 10% Zircopax) was applied inside and partway down the outsides (at the stiff ... more

Wednesday 20th November 2019

The matteness of this glaze depends on the cooling rate

This is the G2934Y matte cone 6 recipe with a red stain (Mason 6021). The one on the left was fired using the C6DHSC slow-cool schedule. The one on the right was fired using the drop-and-soak PLC6DS schedule. The only difference in the two schedules is what happens after 2100F on the way down (the ... more

Wednesday 20th November 2019

What position should the cone be for correct firing?

Four degrees F. These are self-supporting cones, use these. I was consistently getting the cone on the left using a custom-programmed firing schedule to 2204F. However Orton recommends that the tip of the self supporting cone should be even with the top of the base, not the bottom. So I changed the ... more

Wednesday 20th November 2019

The amount of encapsulated stain needed for intense color

This is about 1/2 gallon of glaze with 150 grams of yellow stain ready to mix in. That stain retails for about $30 so its cost alone is about $60 for each gallon (in 2017). But the incredible color it produces cannot be done in any other practical way.

Thursday 14th November 2019

Here is why quartz is good in clay bodies

The piece on the left is 65% ball clay and 35% nepheline syenite. The one on the right is 65% kaolin and 35% nepheline syenite. Both fire vitreous at cone 6. But the glaze is crazing on the kaolin and not on the ball clay. This is because the ball clay contains significant quartz, that raises the thermal expansion and that puts the squeeze on the glaze and prevents the crazing.

Thursday 14th November 2019

A terra cotta body fired from cone 06 (bottom) to 4

Terra cotta bodies are more volatile in the kiln than stonewares. They mature rapidly over a narrower range of temperatures, that process is accompanied by dramatic changes in fired color, density and fired strength. These bars are fired (bottom to top) at cone 06, 04, 03, 02, 2 and 4. This is ... more

Friday 8th November 2019

Four north American ball clays fired to cone 10R, 11 and 10 oxidation

It is amazing now similar different ball clays are. Clearly, soluble salts are an issue with all of them (the brownish scum). These bars are much cleaner on the backsides (since the solubles were left on the surface on the fronts during drying). The drying shrinkages, plasticities and fired maturities are also all remarkably similar.

Thursday 7th November 2019

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