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Tony Hansen's Thousand-Post TimeLine

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


A small laboratory variable speed propeller mixer

If you are at all serious about testing glazes and clay bodies, you need one of these. There are other methods, but nothing else comes close to this. These are expensive new, this one was more than $1000. But you can get them used on I adapted a mount (to give it vertical adjustment) from ... more

Saturday 27th August 2016

N95 Particulate Respirator mask

This designation is an international standard for a general purpose respirator to filter out respirable quartz particles (which cause silicosis). Use one of these when working in a area where ventilation is insufficient to remove all of the dust. Use it also in circumstances where there is temporary ... more

Saturday 27th August 2016

Which tenmoku base is better: Alberta Slip or a clear glaze?

Right: Alberta slip is almost a Tenmoku glaze by itself at cone 10 reduction. To go all the way only 1-2% more iron is needed (plus a little extra flux for melt fluidity, perhaps 5% calcium carbonate). Compare that to crow-baring a clear glaze into a tenmoku (left): This is G1947U plus 11% red iron ... more

Saturday 27th August 2016

Why does this glaze variegate like this?

First, it is thick. "Thick" brings it own issues (like running, blisters, crazing). But look what is under the surface. Bubbles. They are coming out of that body (it is not vitreous, still maturing and generating them in the process). The bubbles are bringing patches of the yellow glass below into ... more

Saturday 27th August 2016

What has this low fire transparent glaze turned blue?

It is made from 85% Ferro Frit 3134, 7.5% kaolin and 7.5% silica. While not obvious from the recipe, one look at the chemistry of this (as displayed when you enter a recipe into your account at will show very low Al2O3. Frit 3134 has almost no Al2O3, yet it is an essential ... more

Thursday 25th August 2016

This appears to be a drying crack, but it is not

This clay normally dries well, but not this time. Strangely, this crack is not at the handle join, it is penetrating into the mug wall. Actually, this is not a crack, it is a split. Excessive slip around the join was not removed, that is bad when a body has larger particles, they permit water left ... more

Thursday 25th August 2016

The green underglaze is failing on impact

This is a low fire fritted stoneware fired to cone 03. But it still has about 4% porosity. The green underglaze is not developing enough glass to bond well with the body surface. Repeated blows to the surface by a hammer are chipping off chunks of glaze/underglaze at the bond with the body. This is ... more

Thursday 25th August 2016

The same liner glaze crazes on the porcelain but not the stoneware

The stoneware has a higher silica content and is not vitreous. This means there are more quartz particles to impose their high expansion because fewer are taken into solution by the feldspar.

Thursday 25th August 2016

What happens when glazes lack Al2O3?

This happens. They are glossy, but lack thickness and body. They are also prone to boron blue clouding (micro crystallization that occurs because low alumina melts crystallize much more readily on cooling). Another problem is lack of resistance to wear and to leaching (sufficient Al2O3 in the ... more

Thursday 25th August 2016

Increasing zircon percentages in a transparent glaze on a brick clay body

These are fired around cone 8. On the far right is 15% zircopax (left has none). Zircon is however very expensive and its use on bricks has to be rationalized, or at least minimized. In this case a white engobe applied first would greatly reduce the zircon percentage needed.

Thursday 25th August 2016

Test, Document, Learn, Repeat in your account at

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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. Download it from the Files panel in your account at (no extra charge).

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What people have said about digitalfire

• Thanks again for a thinking potter's website on glazes - working to take the guess work out of firing results!

• 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'm all right brained..... I have the serial number. My computer is finally going. Thanks for the service. I love my Digital fire.

• I'll be reading and studying for a while, but what is so great is that the information is now right at my finger tips anytime that I need it - its all so very interesting - I never thought that chemistry would ever be interesting, - and I know now very soon I too will be able to slay the glaze dragon!

• Also, as a side note, this website is an excellent resource and I appreciate the fact that all this info is available on the web! Not only that, but I have found the information to be accurate, dependable and thorough, which is difficult to find anywhere.

• Being new to this I was fascinated by the amount of information contained on your website and impressed by what you are willing to share.

• I have found your information extremely helpful - re firing and troubleshooting. Thank you!

• I have used your web sight to help with information for teaching Glaze Formulation. I have sent my students here.

• It would be indeed an honour for me if my contribution in any form can be of any use.

• Thanks for your website! I found it greatly informative and useful in my research work on high temperature ceramic materials.

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