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Tony Hansen's Thousand-Post TimeLine

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


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

Tin oxide can stop the rutile variegation effect dead in its tracks!

This is Alberta Slip (GA6C) on the left. Added frit is melting the Alberta Slip clay to it flows well at cone 6 and added rutile is creating the blue variegated effect (in the absence of expensive cobalt). However GA6D (right) is the same glaze with added Tin Oxide. The tin completely immobilizes the rutile blue effect, it brings out the color of the iron (from the rutile and the body).

Friday 19th August 2016

The classic cone 6 floating blue? No, it is Alberta Slip blue.

And it contains no cobalt! Fairly close in appearance to the classic cone 6 floating blue recipe used across North America, this is a variation of the Alberta Slip Rutile Blue glaze (except this adds 1% tin oxide, 1% black copper oxide and 2% ceramic rutile, it is GA6-C1). Because of the melt ... more

Friday 19th August 2016

How can you make Ravenscrag Floating Blue dance more?

Here it is fired to cone 8 where the melt obviously has much more fluidity! The photo does not do justice to the variegation and crystallization happening on this surface. Of course it is running alot more, so caution will be needed.

Friday 19th August 2016

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What people have said about digitalfire

• 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.

• Very useful articles on practical solutions to the every day problems Ceramic Technicians face in their organizations.

• Thanks, your website is a wealth of information for me and my students.

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

• Great resource!!!

• I love the site. I use it all the time at the Clay Business, and I feel like I have not even touched the surface.

• I have been perusing through some of the level 2 areas of your site and am just in awe of what a great resource you have developed.

• 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.

• I'm still reading about expansion and some of what you explained to me is in this article by digital ... so much lay men terms and analogies makes its more viewable to the mind and understandable... thanks - I continue to say thanks... Tony.... :)

• I am very thankful that you are so good at what you do! Thank you for all your hard work!

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