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Tony Hansen's Thousand-Post TimeLine

I am the creator of Digitalfire Insight, the Digitalfire Reference Database and ... more


Same clay disk dried fast (heat gun) and slower (fan) for the DFAC test

The center portion was protected while the perimeter dried and shrank first (reshaping the central section). No cracks. But as the central area hardened it reached a point where it was stiff enough to impose forces that forced two cracks to start from the outer edge (opposite each other), these grew ... more

Thursday 4th February 2016

Specification for a Tapper Clay lacks physics

Often ceramic clays are described on data sheets primarily by their chemistry (and requested as such). This is typically done at the expense of physical properties data. For example, Tapper clay is employed to plug the drain hole of ladles used to melt metals in the smelting industry. The operators ... more

Thursday 4th February 2016

Newman Red clay fired test bars at a range of temperatures

New is a high temperature red burning fireclay. These fired test bars show how high the iron content is, turning it bright red at all temperatures, even cone 10R (top bar). Other bars are cone 11, 10, 9 and 8 oxidation (top to bottom). Notice it does have some soluble salts that darken the color in reduction.

Wednesday 3rd February 2016

Why did I open this kiln, then push it back in for six weeks!

I love making pottery, but I love the technical side more. I searched for all the test specimens in this load of cone 10 reduction ware first, then pushed it back in and forgot about it. I really anticipate these tests (I am developing and adjusting tons of bodies and glazes at any given time). The ... more

Wednesday 3rd February 2016

Glaze cracking during drying? Wash it off and fix the glaze.

If your dried glaze is doing what you see on the left there is a good chance it will crawl during firing. It is best to wash it off, dry the ware and reglaze. This is Ravenscrag Slip being used pure as a glaze at cone 10R, it is very easy to wash off. To fix this problem I simply add some calcined ... more

Wednesday 3rd February 2016

Another new substitute for G-200 feldspar in North America will be importing this material from India. It will be called Mahavir Potash Feldspar. You can find it in the reference materials in your account. You might like to leave recipes as is (naming G-200 as the material) but insert "Mahavir Potash Feldspar" as the lookup so the chemistry will be correct.

Wednesday 3rd February 2016

Iron oxide goes crazy in reduction

Cone 6 iron bodies that fire non-vitreous and burn tan or brown in oxidation can easily go dark or vitreous chocolate brown (or even melting and bloated in reduction). On the right is Plainsman M350, a body that fires light tan in oxidation, notice how it burns deep brown in reduction at the same ... more

Tuesday 19th January 2016

Translucency of Polar Ice compared to another porcelain at cone 6

On the top you can see the color difference. The other porcelain is made from a low TiO2 mix of typical North American kaolins, feldspars and bentonites. Bottom with a light inside: Polar ice on the left is far more translucent. Yet it is not overly mature, it resists fired warping remarkably well. ... more

Friday 15th January 2016

Compression of the base is the key to avoiding S-cracks? Wrong.

This is an exchange I had on Facebook on this topic. Many people believe cracks are caused by high water content, high shrinkage clay, not compressing the base when throwing, throwing off the hump or stretching the clay excessively when throwing. But I break all these rules every time I make mugs ... more

Friday 15th January 2016

Sixteen kinds of clay. No mugs have cracked in drying. Why?

The key is evenness (in construction and drying process). As you throw the mugs make sure walls are an even thickness put them on a plaster bat (it starts dewatering the base immediately). Make the handles a while after you have made the mugs, they stiffen quicker (in my climate, about an hour). Put ... more

Friday 15th January 2016

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