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Tony Hansen's Thousand-Post TimeLine

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


USGS Mineral Commodity Report

A great reference if you are interested in the supply side of ceramic minerals. Many of the minerals dealt with in this report are ceramics-related. For example, did you know there are 160 companies mining clay in the US! They mine 4.5 million tons (mt) of bentonite, 6mt of kaolin, 1mt of ball clay, 11mt of common clay. What are the ton prices? Check for yourself.

Sunday 11th October 2015

Tin oxide stops crystallization in GA6-A Alberta Slip base glaze

Both of these mugs were soaked 15 minutes at cone 6 (2200F), then cooled at 100F per hour to 2100F and soaked for 30 minutes and then cooled at 200F/hour to 1500F. This firing schedule was done to eliminate glaze defects like pinholes and blisters. Normally the GA6-A glaze crystallizes (devitrifies) ... more

Thursday 8th October 2015

Low expansion version of cone 6 Alberta Slip amber glaze glaze

Alberta Slip with 20% added frit 3134 (left) fired to cone 6 on a porcelain. This is the standard GA6-A recipe. On the right 20% frit 3249 has been used instead. That is a low expansion frit so if you have crazing with the standard recipe, consider trying this one.

Thursday 8th October 2015

Plainsman iron red clays with rutile blue Alberta Slip glaze

Cone 6 mugs made from Plainsman M350 (left) and M390 dark burning cone 6 bodies. The outside glaze is Alberta-Slip-based GA6-C rutile blue and the inside is GA6-A base (20% frit 3134 and 80% Alberta Slip). That inside glaze is normally glossy, but crystallizes to a stunning silky matte when fired using the schedule needed for the rutile blue (cool 100F and soak, slow cool to 1400F).

Thursday 8th October 2015

One example where a highly melt fluid clear glaze is better

On dark burning medium temperature stoneware bodies, clear glazes often do not look good. These bodies contain more raw clays that contain larger particles that generate gases on decomposition during firing. These often cloud up typical clear glazes with micro bubbles, marring their appearance. ... more

Wednesday 7th October 2015

When to use vinegar and when to use epsom salts to flocculate a slurry

Slurries with more clay (like engobes, slips) generally respond better to epsom salts. However the extra clay also makes them more likely to go moldy, so you may need to add a few drops of Dettol to kill the bacteria (if they are stored for any length of time). Vinegar works better for glaze ... more

Saturday 3rd October 2015

Adding water actually made this white engobe run less? How?

The white slip (applied to a leather hard cup) on the left is dripping downward from the rim (even though it was held upside down for a couple of minutes!). Yet that slurry was viscous with a 1.48 specific gravity, on mixer-off the motion stopped immediately. Why? Because it was not thixotropic (it ... more

Saturday 3rd October 2015

I want this engobe to gel in ten seconds. Why?

It is going to be applied to leather hard earthenware and it needs to be thixotropic. Why? I do not want it to run down from the rims of the mugs after dipping. The process: Stir the engobe, pour-fill the mug, pour it out and push it upside down into the engobe. If I can pull it back out before the ... more

Saturday 3rd October 2015

White spots and blisters in a high zircon glaze at cone 6

This is also a common problem at low fire on earthenware clay, but in this case it is on a buff stoneware. Those white spots you see on the beetle also cover the entire glaze surface (although not visible). They are sites of gas escaping (from particles decomposing in the body). This is happening on ... more

Saturday 3rd October 2015

Two transparent glazes on the same clay. Why different?

The transparent glaze on the outside of the left cone 6 mug is fluid and runny. It is able to clear the micro-bubbles during firing. The glaze on the right, although it fires to a brilliant glossy surface on porcelain or buff stoneware, clouds up with tiny bubbles and has lost the glassy surface when used with this red burning clay.

Saturday 3rd October 2015

Conquer the Glaze Dragon With Digitalfire Reference info and software

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Interactive ceramic glaze chemistry calculations.

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Chemistry plus physics. This is about your data!

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