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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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Here is what digitalfire.com looked like in 1997!

Here is what digitalfire.com looked like in 1997!

We already had a large library of educational material (the predecessor of the Digitalfire Reference Library). The Foresight product was the fore-runner to insight-live.com today. And it was free like today. And we were warning people about the importance of safe glazes and understanding the "why" questions about the ceramic process.

Thursday 18th January 2018

Matte cone 6 glazes have identical chemistry but one melts more. Why?

Matte cone 6 glazes have identical chemistry but one melts more. Why?

These are 10 gram balls that we melted on porcelain tiles at cone 4 (top two) and cone 6 (bottom two). They compare the melt fluidity of G2934 (left) and G2934Y (right). The Y version sources its MgO from frit and talc (rather than dolomite). It is a much more fluid melt because the frit is yielding ... more

Thursday 11th January 2018

Cobalt and iron overglazes bleeding into the matte glaze

Cobalt and iron overglazes bleeding into the matte glaze

This is the G2934Y matte base with overglaze decoration fired at cone 6. Although this matte has a high melt fluidity, overglaze decoration can be successful as long as it is not applied too thick and not overfired. But in this case the glaze is thickly applied. Once the critical thickness boundary ... more

Thursday 11th January 2018

The value of a white vitreous engobe over terra cotta at cone 03

The value of a white vitreous engobe over terra cotta at cone 03

At cone 03 many terra cottas will fire quite dense and stoneware-like. The lip of the mug on the left is covered with a vitreous white engobe (L3685U) under the glaze (G1916Q). Red bodies are much stronger at low temperatures, but do not lend themselves well to the bright glaze colors that work so ... more

Thursday 11th January 2018

Why you should not paint pure stain powders over glaze

Why you should not paint pure stain powders over glaze

On the left is a pure blue stain, on the right a green one. Obviously, the green is much more refractory. On the other hand, the green just sits on the surface as a dry, unmelted layer. For this type of work, stains need to be mixed into a glaze-like recipe of compatible chemistry (a medium) to ... more

Thursday 11th January 2018

How to convert a dipping glaze to a brushing glaze

How to convert a dipping glaze to a brushing glaze

I have a jar of testing clear glaze that I mixed myself (10% yellow stain and 2% zircopax added to cone 03 G2931K clear). Commercial glaze producers make their lines of glazes like this. The cost of the dry materials: About $6. How can I convert it to a paintable glaze like the commercial ones? I ... more

Saturday 6th January 2018

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 my clear glaze liquid slurry (recipe G2926B). I dried it out under a heat lamp and weighed it again (top left). I have filled those two weights, 8.9 and ... more

Friday 5th January 2018

The language of art will never adequately describe this issue or its solution

The language of art will never adequately describe this issue or its solution

This is crazing. It is bad on functional ware. Shivering and leaching are also bad. And blistering. And other problems like devitrification and clouding compromise the visual appearance of ware. Science is needed to understand what these are, how serious they are and determine the cause and ... more

Monday 1st January 2018

Refiring a terra cotta mug that had already bubbled only made it worse

Refiring a terra cotta mug that had already bubbled only made it worse

Plus the glaze ran even more. The main problem was that the original firing was taken too high, about cone 02 (seven hour schedule). This body nears zero porosity there and is beginning to decompose. That generates gases. The second firing was taken to cone 03 in four hours. But the glaze just ... more

Sunday 31st December 2017

A high expansion glaze is bowing the foot of the bottom bowl

A high expansion glaze is bowing the foot of the bottom bowl

The glaze has a calculated thermal expansion of 8.8 (because of high KNaO and low SiO2). Very high. It is basically stretched on. These plates are not glazed on the bottom. The glaze on the inside of the upper plate fits, the base is flat. But the glaze on the inside of the lower plate is pulling ... more

Saturday 23rd December 2017

Test, Document, Learn, Repeat in your account at insight-live.com

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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.

Conquer the Glaze Dragon With Digitalfire Reference info and software

Still available for Mac, PC, Linux

Interactive glaze chemistry calculations.


How to reach us

From within your account at Insight-Live.com or

What people have said about digitalfire

• I have been in the pottery business for 52 years, Pemco use to be 10 miles from us. Your advise on solving our glaze problem worked perfectly and you explained it so well. I have had this problem for 7 years, re-firing lots of ware. Pemco guys and Pfaltzgraff Pottery glaze dept. told me different recipes but it never solved the problem. None of them talked about firing cycles. Tony, how did you get so smart? God has Blessed you.

• I am so fascinated by your site I have trouble to leave it!

• You have been more than helpful and I will recommend your site to all of my pottery friends. Once again a big thank you.

• I think Glaze chemistry is an extremely under-appreciated and under-estimated field of science.

• Nice to know you are out there to lend us a hand. You are very much appreciated by this potter and many more, I am sure.

• I have been studying your web site and which I have found extremely helpful for someone like me who is not a chemist!

• So far your site has been a blessing in that I don't feel I have to go anywhere else to get my information, you have it all (at least as far as I can see now) right here in one place. I am new to glaze formulation but not to ceramics. Recently I have had a crazing problem with a certain clay body I am using and as of today I feel confident I can solve it using information on your website. It is I who want to thank you for making such a clear and concise information depository that can be used by all, especially those new to glaze chemistry.

• Hi Tony, Thanks for this great project and all the info and tutorials.

• I would love to take a trip inside of your brain. I am sure that it would be a fantastic light show.

• I love your site and am so grateful for all you have done to help with glaze formulation/safety.


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