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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.


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What people have said about digitalfire

• Thank you for Digital Fire!!! Your site and your program are wonderful, thank you for the resource!!

• Firstly, I want to thank you about this very good site in the net which helps very much in the development of the ceramics industry.

• I normally do not comment on articles I find, but this is amazing. Thank you so much for providing this information! I am a ceramics student in my BFA year, and this is the most comprehensive and helpful information I have found on creating a porcelain casting slip.

• You are so good for me. Find a stumbling stone and in a moment the path is easier.

• Most of the compositions came from the Digitalfire Ceramic Materials site, to which all who analyze glazes owe a debt of gratitude.

• Hello. I simply wanted to say thank you very much for providing me with so much important information.

• What a great site! Such a wealth of information. The thing I appreciate most about the site is the orderly and thoughtful and thought through approach to glazing. We are learning and earning potters, learning the craft and acquiring some income from it as we grow, working with cone 6 clays and glazes. I've been visiting your site frequently recently because we are starting to mix our own glazes, and we wanted to be able to incorporate the textures, surfaces and colors of our choosing, not hit or miss due to trying untold numbers of blind recipes. I've found that even a glaze that I've seen on someone else's work, using the same glaze mix on my work, does not guarantee the same result in my kiln, due to clay differences, surely, but also how my kiln fires, what temps it reaches, what timing, etc. So we want be able to work out glazes that look and feel the way that we like, in our firing environment, on our clays.

• Tony, the Boraq II substition for gerstley borate in the formula I sent you a while ago was succesful. Congratulations for figuring out boraq! I've tested Murray's, Gillespie, Laguna, IMCO, and also raw materials such as Cadycal, Ulexite, Colemanite, and the substitutes you recommended in your articles made of several components blended with Cadycal (I referred to these in my previous letter) all with varying degrees of success but only the boraq II produced results that were indistinguishable from GB. This glaze is very sensitive so I consider the test a success. It had to mess with the plasticity with additions of hectorite and ball clay.

• Again, thanks for being such a resource to potters over the years!

• Your website's a great help to ceramic beginners. Keep up the good work.


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