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Tony Hansen's Thousand-Post TimeLine

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

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G2934 vs. G2934Y cone 6 yellow mattes

G2934 vs. G2934Y cone 6 yellow mattes

They have the same chemistry, but Y, on the right, sources MgO from a frit rather than from dolomite. Y is has a more fluid melt so it is not as opaque against the black slip underneath (thus it looks better on translucent porcelains). However its surface is just slightly finer. The Y one appears ... more

Saturday 11th November 2017

Smash your ware to see if it is strong!

Smash your ware to see if it is strong!

I use a nylon hammer, and glasses of course. I just filled two five-gallon pails and three boxes. Every type of clay and glaze I currently use. Every temperature. I started with a commercial Denby stoneware piece to get a feel for how quality ware should break. It becomes immediately evident which ... more

Saturday 11th November 2017

Soluble ingredients in glazes always precipitate as angular crystals. Right?

Soluble ingredients in glazes always precipitate as angular crystals. Right?

Wrong. These tiny spheres (actually they are not so tiny) form over time as a precipitate in a glaze having a high concentration of a boron frit and mixed in hard water. This may be an example of how interactions can affect the degree to which materials dissolve in water (in this case the electrolyte in the water could be a trigger). These are likely ooids.

Friday 10th November 2017

Are frits partially soluble? Yes, many are.

Are frits partially soluble? Yes, many are.

These 1 mm-sized crystals were found precipitated in a couple of gallons of glaze containing 85% Ferro Frit 3195. They are cubical, hard and insoluble. Why and how to do they form? Many frits are slightly partially soluble and the degree to which they are are related to the length of time the glaze ... more

Friday 10th November 2017

When two clays are joined are they compatible?

When two clays are joined are they compatible?

These bi-body strips are made by rolling two clays together in a thin sandwich. Three porcelains are being compared to a very plastic grogged sculpture body. After drying (top) they curl a little, two toward the sculpture body and one, the most plastic of the porcelains, toward the white. But on ... more

Friday 10th November 2017

Gradient bars show the degree of vitrification of a clay

Gradient bars show the degree of vitrification of a clay

These are the fronts and backs of dust-pressed bars. After final drying the width at each line is carefully recorded. They are fired horizontally in a furnace able to reproduce linear thermal gradients along the length of the bar. Thermocouples monitor the temperatures along the bar, so the ... more

Friday 10th November 2017

A vessel being forced apart by the pressure of a low expansion glaze inside

A vessel being forced apart by the pressure of a low expansion glaze inside

Many people would find the fired appearance of this cone 10 reduction red fireclay (Plainsman FireRed) compelling. But it is not at all suitable for functional ware. This crack grew wider over a period of a week (after firing) because the inside glaze is exerting forces it cannot resist. Notice that ... more

Thursday 9th November 2017

The difference between vitrified and sintered

The difference between vitrified and sintered

The top fired bar is a translucent porcelain (made from kaolin, silica and feldspar). It has zero porosity and is very hard and strong at room temperature (because fibrous mullite crystals have developed around the quartz and kaolinite grains and feldspar silicate glass has flowed within to cement ... more

Thursday 9th November 2017

The glaze broke the pot!

The glaze broke the pot!

A example of a highly fluid cone 6 glaze that has pooled in the bottom of a mug (and crystallized). It has caused a crack all the way around that has separated the base. Glazes normally need to be under some compression to avoid crazing (by having a lower-than-the-body thermal expansion), but if ... more

Thursday 9th November 2017

Why would a low fire transparent require four frits?

Why would a low fire transparent require four frits?

To get the needed chemistry to avoid boron blue clouding (calcium borate crystals). The one on the right clouds, the other does not. Why? Differences in the chemistry (as seen in my account at insight-live.com). G2931K, on the left, has greater Al2O3 (which impedes the growth of crystals), lower CaO ... more

Thursday 9th November 2017

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Interactive glaze chemistry calculations.


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