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Tony Hansen's Thousand-Post TimeLine

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


A novel way to compare degree of porcelain vitrification

These two unglazed porcelain tiles appear to have a similar degree of vitrification, but do they? I have stained both with a black marker pen and then cleaned it off using acetone. Clearly the one on the right has removed better, that means the surface is more dense, it is more vitreous. In industry ... more

Wednesday 20th July 2016

G3806C Transparent with Copper Oxide at cone 6

This is not just a typical transparent cone 6 glaze with copper added. Knowing what is different about this clear base, its trade-offs and how it was developed are important. The porcelains are Plainsman P300 and M370. The liner glossy glaze is G2926B, it has a much lower melt fluidity than the ... more

Tuesday 19th July 2016

A sculpture bodies gets a lot more interesting surface

This is an example of how soluble salts can enhance the appearance of the fired surface of a cone 10R clay. This sculpture body is a vitreous dark brown burning base having lighter colored 20 mesh grog particles. The one on the left uses native stoneware clays that contain natural flux-containing ... more

Tuesday 19th July 2016

The texture of 33% 20-48 mesh grog in a flameware body

The body is a 50:50 talc:ball clay mix, it is very smooth and slick so the only particulate is from the grog. In this case the grog addition is being used to make the body resistant to thermal shock failure (for use as a flameware). The body itself is not low expansion nor are the grogged particles. ... more

Tuesday 19th July 2016

Grog does not always have the intended effect

These DFAC drying performance disks show that minor additions of grog do not reduce the fired shrinkage of this medium fire stoneware much. Nor do they improve its drying performance. In this example, a 10% addition has not reduced shrinkage appreciably nor has it improved drying performance. The ... more

Tuesday 19th July 2016

A limit or target glaze formula. What does this mean?

Formulas list oxide molecules and their comparative quantities. Oxides construct the fired glass. The kiln de-constructs ceramic materials to get the oxides, discards the carbon and builds the glass from the rest. You can view glazes as recipes of materials or as formulas of oxides. Why use ... more

Wednesday 13th July 2016

Can you actually throw a Gerstley Borate glaze? Yes!

Worthington Clear is a popular low fire transparent glaze recipe. It has 55% Gerstley Borate plus 30% kaolin (Gerstley Borate melts at a very low temperature because it sources lots of boron). GB is also very plastic, like a clay. I have thrown a pot from this recipe! This explains why high Gerstley ... more

Friday 8th July 2016

Same cone 6 glazes. Same clay. Why is the one on the right pinholing?

These are thick pieces, they need time for heat to penetrate. Both were soaked 15 minutes at cone 6 (2195F in our test kiln). But the one on the left was control-cooled to 2095F degrees and soaked 45 more minutes. Pinholes and dimples are gone, the clay is more mature and the glaze is glossier and ... more

Friday 8th July 2016

Reduction and oxidation porcelains

Left: Cone 10R (reduction) Plainsman P700 porcelain (made using Grolleg and G200 Feldspar). Right: Plainsman Cone 6 Plainsman Polar Ice porcelain (made using New Zealand kaolin and Nepheline Syenite). Both are zero porosity. The Polar Ice is very translucent, the P700 much less. The blue coloration ... more

Wednesday 29th June 2016

Are frits partially soluble? Yes, many are.

These 1 mm-sized crystals were found precipitated in a couple of gallons of glaze containing 85% Ferro Frit 3195. They are hard and insoluble. Why and how to do they form? Many frits are slightly partially soluble and the degree to which they are are related to the length of time the glaze is in ... more

Tuesday 28th June 2016

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

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• I have read just about all your articles on Digitalfire and use your software, really appreciate the wealth of knowledge and testing you bring to ceramics.

• Your resources are truly amazing and as an ex electronic engineer (now a potter), I really am impressed with your analytical approaches. Your site is almost a complete college level course on pottery (less the throwing & handbuilding). Thank you for your wonderful contributions.

• Thank you for this article. I learned more about the science in this one article (What is Deflocculation) than I have in the last 40 years of classes and conversations. Truly enjoyed this.

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• What an awesome list of videos you have here, and the info on your site is invaluable.

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