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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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Transparent and RavenTalc silky matte glazes on black engobe at cone 10R

Transparent and RavenTalc silky matte glazes on black engobe at cone 10R

Clay is Plainsman H450. The L3954N black engobe was applied at leather hard stage (on the insides and partway down the outside). The G1947U clear glossy glaze over it on the inside produces a deep and vibrant hue (left). The inside glaze on the right is GR10-C Ravenscrag silky matte. The outsides are GR10-J Ravenscrag Dolomite matte with a little added cobalt and iron (for blue and brown).

Wednesday 20th March 2019

Difference between oxidation and reduction! GR10-C matte on Plainsman H443

Difference between oxidation and reduction! GR10-C matte on Plainsman H443

Same body, same glaze. Left is cone 10 oxidation, right is cone 10 reduction. What a difference! This is a Ravenscrag-Slip-based recipe on a high-fire iron stoneware. In reduction, the iron oxide in the body and glaze darkens (especially the body) and melts much more. The behavior of the tin oxide opacifier is also much different (having very little opacifying effect in reduction).

Wednesday 20th March 2019

Plainsman iron red clays with rutile blue Alberta Slip glaze

Plainsman iron red clays with rutile blue Alberta Slip glaze

Cone 6 mugs made from Plainsman M350 (left) and M390 dark burning cone 6 bodies. The outside glaze is Alberta-Slip-based GA6-C rutile blue and the inside is GA6-A base (20% frit 3134 and 80% Alberta Slip). That inside glaze is normally glossy transparent amber, but crystallizes to a stunning silky matte when fired using the C6DHSC schedule (cool 100F and soak, slow cool to 1400F).

Wednesday 20th March 2019

Sourcing Li2O from spodumene instead of lithium carbonate

Sourcing Li2O from spodumene instead of lithium carbonate

Lithium carbonate is now incredibly expensive. But I was able to source the Li2O from spodumene instead. Spodumene has a complex chemistry, but the oxides that it contains (other than Li2O) are those common to glazes anyway. Using my account at insight-live.com, I did the calculations and got a ... more

Tuesday 19th March 2019

Here is why quartz is good in clay bodies

Here is why quartz is good in clay bodies

The piece on the left is 65% ball clay and 35% nepheline syenite. The one on the right is 65% kaolin and 35% nepheline syenite. Both fire vitreous at cone 6. But the glaze is crazing on the kaolin and not on the ball clay. This is because the ball clay contains significant quartz, that raises the thermal expansion and that puts the squeeze on the glaze and prevent the crazing.

Tuesday 19th March 2019

Functional ware at low fire! Don't dismiss it just yet.

Functional ware at low fire! Don't dismiss it just yet.

These were only fired at cone 04, but they are durable enough to last some time with normal use. The insides have a transparent glaze (Spectrum 700), it is leadless and completely safe. These are great insulators, they keep coffee warm longer than porcelain or stoneware. The feet are glazed so they ... more

Monday 18th March 2019

Which is better for functional ware? Cone 04? Cone 10 reduction?

Which is better for functional ware? Cone 04? Cone 10 reduction?

Not so fast! Cone 10R ware is only strong if the glaze fits. Fortunately this does. But either one will break if dropped on the floor. The stoneware clay has a porosity of 2.5-3%, the earthenware 12%. But the entire base of the orange one is glazed (it was fired on a three-pointed stilt), and the ... more

Monday 18th March 2019

The matteness this glaze develops is dependant on the cooling rate

The matteness this glaze develops is dependant on the cooling rate

This is the G2934Y matte cone 6 recipe with a red stain (Mason 6021). The one on the left was fired using the C6DHSC slow-cool schedule. The one on the right was fired using the drop-and-soak PLC6DS schedule. The only difference in the two schedules is what happens after 2100F on the way down (the ... more

Wednesday 13th March 2019

Cheap Amazon glaze mixer, how does it stack up?

Cheap Amazon glaze mixer, how does it stack up?

Make some adjustments and it is usable. First, it is very quiet and has lots of power. The plastic sliders ride smoothly and provide precise adjustability (but the plastic threads might not last). The vertical shaft is stainless steel and the cast iron base is heavy, sturdy, practical. The ... more

Tuesday 12th March 2019

It's possible to formulate a porcelaineous stoneware with just two materials

It's possible to formulate a porcelaineous stoneware with just two materials

Left: 65% #6Tile kaolin and 35% Nepheline Syenite. It's white but crazes the glaze and has 1% fired porosity (measured in the SHAB test) so it does not have porcelain density. Plasticity is very good. Right: 65% M23 Old Hickory ball clay and 35% Nepheline Syenite. The glaze fits, it has zero ... more

Monday 11th March 2019

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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 (legacy, no longer supported)


What people have said about digitalfire

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• Where have I been. I could have used this site about a thousand times and would have saved myself about a thousand hours over the past years had I been aware of the remarkable information provided here.

• LOVE your site! You have saved me a whole lot of work and research time with your materials data base and comments. I haven't gotten to explore your software yet because I'm in the middle of resolving another mess involving raw materials from a certain large company with sloppy production. We are a small company that is developing a low expansion, thermal shock resistant porcelain for industrial use ... Between our acquired data and some clues contained in your comments we were able to pin point the problem.

• Thank you for your support, it is wonderful and appreciated.

• '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!"

• I would like to stay connected to your program. In my glaze workshops, I use your 5/20 glaze as our Cone 6 reference so I often mention you and Digital Fire.com to all of my students. I also tell them about all the great articles and reference materials you have with the level 2 program.


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What people have said about Insight-Live

• I have really been enjoying using insight.

• Thank you very much for your website, as a amateur Potter I find it an incredibly useful source of information about all kinds of things pottery related and when I'm trying to make glazes for example I will often refer to your website for guidance.

• Hey Tony, thanks so much for developing such a useful software. I have come to digital fire for countless questions I have had with clay and glazes.

• Awesome site...you do great work!

• Thank you for your incredible library of information. I have a background in QA (Six Sigma) and Biology so I genuinely appreciate the information you've made easily accessible.

• I write to appreciate your good works by way of the articles you made available on the net .. Thanks a million for your good work. From Nigeria.

• I want to first tell you that your site is amazing. i love the approach, the attitude, and the incredible information. the fact taht you share so much of your information to the public is truly wonderful. I recenly fell in love with ceramics and set up a home studio.


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