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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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A settling, running glaze recipe gets a makeover

The original cone 6 recipe, WCB, fires to a beautiful brilliant deep blue green (shown in column 2 of this Insight-live screen-shot). But it is crazing and settling badly in the bucket. The crazing is because of high KNaO (potassium and sodium from the high feldspar). The settling is because there ... more

Monday 13th February 2017

Glazes of the same chemistry: The fritted one melts better

It seems logical (and convenient) to just say that the kiln does not care what materials source the oxides in a glaze melt. Li2O, CaO, Al2O3, SiO2 are oxides (there are about ten common ones). The kiln just melts everything and constructs the glaze from the ones available. Right? Wrong! Things get ... more

Monday 13th February 2017

Severely cutlery marking in a glaze lacking sufficient Al2O3

The glaze is cutlery marking (therefore lacking hardness). Why? Notice how severely it runs on a flow tester (even melting out holes in a firebrick). Yet it does not run on the cups when fired at the same temperature (cone 10)! Glazes run like this when they lack Al2O3 (and SiO2). The SiO2 is the ... more

Friday 10th February 2017

Al2O3 in glazes make them durable and wear resistant

The cone 6 glazes on the left have double the boron of those on the right so they should be melting much more. But they flow less because they have much higher Al2O3 and SiO2 contents. This effect renders them milky white vs. the transparent of those on the right. Why? Because G and H are trapping ... more

Friday 10th February 2017

Cutlery marking is directly related to the chemistry of the glaze

This is an example of cutlery marking in a cone 10 silky matte glaze lacking Al2O3, SiO2 and having too much MgO. Al2O3-deficient glazes often have high melt fluidity and run during firing, this freezes to a glass that lacks durability and hardness. But sufficient MgO levels can stabilize the melt ... more

Friday 10th February 2017

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

Friday 10th February 2017

Example of a whole rock chemical analysis lab report

Powdered samples were sent to the lab. The numbers shown on this report are in percentage-by-weight. That means, for example, that 15.21% of the weight of the dry powder of Alberta Slip is Al2O3. Insight-live knows material chemistries in this way (whereas desktop Insight needs them as formulas). ... more

Friday 10th February 2017

Crawling sanitary ware glaze sourcing Al2O3 from only feldspar

The original recipe had a very low clay content, sourcing almost all of its Al2O3 from feldspar instead. Although the glaze slurry was maintained at 1.78 specific gravity (an incredibly high value) and thus would have had very low shrinkage, it did not stick and harden well enough to the ware. Why? ... more

Friday 10th February 2017

Potters can learn from how glazes are fit on ceramic tile

These are thermal expansion curves for body, engobe and glaze (from a dilatometer, a device that measures it against increasing temperature). The upper line is the body. The center line is the engobe. The lower line is the glaze. The ceramic tile industry is very conscious, not only of glaze-fit but ... more

Thursday 2nd February 2017

A casting slip of 1.9 specific gravity. Should we use it?

A hydrometer is being used to check the specific gravity of a ceramic casting slip in a graduated cylinder. Common traditional clay-containing ceramic slips are usually maintained around 1.75-1.8. In this case the slurry was too heavy, almost 1.9. Yet it is very fluid, why is this? It has both too ... more

Monday 30th January 2017

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Interactive glaze chemistry calculations. Download it from the Files panel in your account at Insight-live.com (no extra charge).


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What people have said about digitalfire

• Your web is great!

• 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

• As a new potter, your website has been an incredible source of information for me, both in tips, recipes and things to ponder. I know I can speak for a few others when I say please keep posting as the information is highly valued.

• I want you to know how much it means to me to have you help with my questions. I have been doing pottery for over 20 years and never new this stuff. I feel so responsible for my glazes leaching and stupid to not have known, and the stress or waiting for the lab test results has been eating me up.

• This is a excellent site for Ceramic colors and containing very good knowledge for Ceramic coloring agents. Thank to Digitalfire Ceramic Oxides Directory.

• I have been thinking to thank you for the great help your interest in ceramics continues to inspire in my studio.

• Wow. Thanks. That is so great. I also thank you for making so much material available on your web site. You obviously care deeply about the craft and teaching others.

• 'we have been using the arabia blue and white variation of the 5X20 cone 6 glaze, and have had a great response from our customers. Thanks for your efforts - you have made a believer out of me!"

• Go look at Tony Hansens page and look at Insite. Incredible amounts of information. He has a great explanation of .. Shivering ---and the opposite----- Crazing. Cause and solution.

• Your materials database has been the best source of information for me for a long time. Even most of the European frits are in there and this is not true for many books.


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