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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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These two frits have one difference in the chemistry: Al2O3.

These two boron frits (Ferro 3124 left, 3134 right) have almost the same chemistry. But there is one difference: The one on the right has no Al2O3, the one on the left has 10%. Alumina plays an important role (as an oxide that builds the glass) in stiffening the melt, giving it body and lowering its ... more

Thursday 20th April 2017

How to make a ceramic time-bomb

This mug is pinging loudly and literally self-destructing in front of my eyes! Why? The glaze is under so much compression (the inside is pushing outward, the outside inward). Spiral cracks are developing all the way up the side. Small razor-sharp flakes are shivering off convex contours. Why? I ... more

Sunday 16th April 2017

Example of how bubbles dissipate in a glaze with increasing temperature

This is a Gerstley Borate based recipe (45%) melted in crucibles at increasing temperatures. Although the recipe is well melted at cone 2, it is still not fluid enough to enable their migration in the time available. By contrast, the melt at the upper temperature is much less viscous, enabling all ... more

Sunday 16th April 2017

Ceramic Oxide Periodic Table

All common traditional ceramic base glazes are made from only a dozen elements (plus oxygen). Materials decompose when glazes melt, sourcing these elements in oxide form. The kiln builds the glaze from these, it does not care what material sources what oxide (assuming, of course, that all materials ... more

Wednesday 12th April 2017

Insight-Live comparing a glossy and matte cone 6 base glaze recipe

Insight-live is calculating the unity formula and mole% formula for the two glazes. Notice how different the formula and mole% are for each (the former compares relative numbers of molecules, the latter their weights). The predominant oxides are very different. The calculation is accurate because ... more

Wednesday 12th April 2017

Same high-iron glaze. One crystallizes and the other does not. Why?

Both mugs have the same cone 6 oxidation high-iron (9%), high-boron, glossy glaze. Iron silicate crystals have completely invaded the surface of the one on the right, turning the near-black glossy into a yellowy matte. Why? Three things. It was slow-cooled and the other free-fall-cooled (firings ... more

Wednesday 12th April 2017

Solving a difficult engobe flaking problem

This demonstrates the difficulty you can encounter when trying to get an engobe working with a clay body. Here the slip/glaze is flaking off the rim of pieces at cone 04 (does not happen at 06). The front bi-clay bar demonstrates the white and red clays dry well together (the slight curve happened ... more

Tuesday 11th April 2017

How can you test if an engobe fits your clay body?

This is part of a project to fit a fritted vitreous engobe (slip) onto a terra cotta at cone 02 (it fires harder there). Left: On drying the red body curls the bi-clay strip toward itself, but on firing it goes the other way! Right: Test bars of the white slip and red body compare their drying ... more

Tuesday 11th April 2017

Bi-Clay strips test compatibility between engobe and body

Slips and engobes are fool-proof, right? Just mix the recipe you found on the internet, or that someone else recommends, and you are good to go. Wrong! Low fire slips need to be compatible with the body in two principle ways: drying and firing. Terra cotta bodies have low shrinkage at cone 06-04 ... more

Tuesday 11th April 2017

Yikes. Cutlery marking this bad on a popular glaze!

An example of how a spoon can cutlery mark a glaze. This is a popular middle temperature recipe used by potters. The mechanism of its matteness is a high percentage of zinc oxide that creates a well-melted glaze that fosters the growth of a mesh of surface micro-crystals. However these crystals ... more

Monday 10th April 2017

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What people have said about digitalfire

• When my group of potters are pressed to improve our glazes they say if the old way is not broken yet why don't you buy yourself some kind of a kit to play with new glazes and then we can make it for everyone. You got to be kidding I say to myself. Anyway, your website will help me help the group out of some old and boring glazes if I can see forward enough. Thanks for all this important info, I can't believe this website is here!

• Just wanted to tell you I just found your site and find it extremely useful. Got it bookmarked and will be referring to it frequently. Great job! Thank you!

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

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

• THANKS so much for all of the information you share at no cost. It really helps me. I feel a little guilty for not subscribing to Insight, but I am working toward that. You have truly changed the way I think about glaze, and I appreciate you. thanks. future subscriber/fledgling potter

• After perusing your site for some time, I am really getting the sense of what a valuable resource it is. Thank you for it.

• I enjoy and appreciate your work very much.

• I knew nothing about chemistry, so I have already learned a great deal from the information you've so generously provided on-line.

• I want to also thank you for all you have done for the ceramic and pottery industry.

• 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.


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