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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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The high thermal expansion of a low-fire talc body

The high thermal expansion of a low-fire talc body

Talc is employed in low fire bodies to raise their thermal expansion (to put the squeeze on glazes to prevent crazing). These dilatometer curves make it very clear just how effective that strategy is! The talc body was fired at cone 04, the stoneware at cone 6. The former is porous and completely ... more

Wednesday 11th October 2017

Three low fire bodies need three different clear glazes. Why?

Three low fire bodies need three different clear glazes. Why?

Glaze fit. The left-most clay mug contains no talc (Plainsman Buffstone), the centre one about 25% talc (L212) and the right one is about 45% talc (L213). Talc raises thermal expansion. The centre glaze is G2931K, it is middle-of-the-road thermal expansion (Insight-live reports it as 7.4) and fits ... more

Sunday 8th October 2017

Plucking on a vitreous porcelain at cone 6

Plucking on a vitreous porcelain at cone 6

The mug on the left is made from a whiteware body (Plainsman M370), the one on the right is a highly vitreous translucent one (Plainsman Polar Ice). Both have been over-fired slightly. The Polar Ice mug has stuck to the shelf somewhat, taking chips out of the base on the outer perimeter of the bare ... more

Wednesday 4th October 2017

The foot ring on the left is plucking, the right one is not. Why?

The foot ring on the left is plucking, the right one is not. Why?

These are translucent porcelains, they are vitreous. The firing is to cone 10. The one on the left is a cone 6 body, and, while it survives to cone 10 it does warp. But more important, it is much more vitreous (more melted). The plucking problem makes it quite difficult to get a good foot ring. The ... more

Wednesday 4th October 2017

A black engobe transforms the floating blue glaze over it

A black engobe transforms the floating blue glaze over it

M340 stoneware fired to cone 6 (drop-and-hold schedule). The L3954B engobe fires deep black (it has 10% Mason 6600 black stain instead of the normal 10% Zircopax). It was applied inside and partway down the outside (a much less messy process than using a black clay body). They were bisque fired and ... more

Monday 2nd October 2017

Dark Umber-Stained Engobes on M340 at cone 6

Dark Umber-Stained Engobes on M340 at cone 6

This is the standard Plainsman L3954D white engobe recipe with the 10% Zircopax switched for Burnt Umber. The result is a dark, rich, ultra-gloss brown (almost black). The engobe is applied inside and half-way down the outside. The mug on the left is glazed inside and out with the base GA6A Alberta ... more

Monday 2nd October 2017

Measuring glaze slurry specific gravity

Measuring glaze slurry specific gravity

This is the easiest way to measure the specific gravity of a glaze if it is not in a container deep enough to float a hydrometer (or if it is too thick to float it properly). Just counterbalance the empty graduated cylinder to zero, fill it to the 100cc mark and the scale reads the specific gravity. ... more

Friday 22nd September 2017

6% rutile is too much in this cone 6 oxidation glaze

6% rutile is too much in this cone 6 oxidation glaze

Rutile variegates glaze surfaces. But it also opacifies at higher percentages. The blue effect is a product of crystallization that occurs during cooling, it is thus dependent on a slower cooling cycle, especially above 1400C. This is GA6-C Alberta Slip glaze with 4, 5 and 6% rutile. At 6% the ... more

Thursday 21st September 2017

How to convert a dipping glaze to a brusing glaze

How to convert a dipping glaze to a brusing glaze

I have a jar of clear glaze that I mixed myself (it has 10% yellow stain and 2% zircopax added). The cost of the dry materials: About $6. How can I convert it to a paintable glaze like the commercial ones I buy for $20 a jar? I made a spreadsheet to do it for me. It knows the weight of the plastic ... more

Wednesday 20th September 2017

I have 161 grams of stain. I need to mix it into how much clear glaze slurry?

I have 161 grams of stain. I need to mix it into how much clear glaze slurry?

Stain powders are expensive. I want to make as much glaze as I can from every gram of this red stain I have at hand. I have weighed a teaspoon of the liquid slurry, dried it out under a heat lamp and weighed it again (top left). I have filled those two weights, 8.9 and 4.74, into a spreadsheet I ... more

Wednesday 20th September 2017

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Chemistry plus physics. The on-line successor to desktop Insight. Get an account for as little as $15. It does so much more.

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