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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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Measure glaze specific gravity with these? Forget it!

Measure glaze specific gravity with these? Forget it!

Glazes need to be gelled, have thixotropy. That means these things won't bob up and down to find the right place. The one on the right is completely useless, the scale is too wide. Most glazes need to be between 1.4 and 1.5 specific gravity (40-50 on this scale). That is like reading seconds on the ... more

Wednesday 16th August 2017

How to make a ceramic time-bomb

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

Tuesday 15th August 2017

Drip glazing and bare outsides: Deceptively difficult.

Drip glazing and bare outsides: Deceptively difficult.

Why? Glaze fit. These are available on Aliexpress (as Drip Pottery) and they are made by a manufacturer that has a dilatometer to precisely match the thermal expansion of the glaze with the body. The inside glaze has to fit better than normal because of the absence of an outside glaze. Too low of a ... more

Monday 14th August 2017

Glaze at 1.7 specific gravity on green-ware. Way too thick!

Glaze at 1.7 specific gravity on green-ware. Way too thick!

This is G2926B clear cone 6 glaze deflocculated with Darvan. Because the Darvan is thinning it, 2.5kg of powder is suspended in only 1100 grams of water (half the normal amount). While the slurry in the bucket flows well and appears like it should work, a one-second dip produces twice the desired ... more

Monday 14th August 2017

Why you should not paint pure stain powders over glaze

Why you should not paint pure stain powders over glaze

On the left is a blue stain, right is a green. Obviously the blue is melting much better, even bleeding at its edges. On the other hand, the green just sits on the surface as a dry, unmelted layer. For this type of work, stains need to be mixed into a glaze-like recipe of compatible chemistry (a ... more

Saturday 12th August 2017

Mug made from a cone 6 black-burning stoneware body

Mug made from a cone 6 black-burning stoneware body

Black burning bodies are popular with many potters. They are normally manufactured by adding around 10% burnt or raw umber to an existing buff-burning cone 6 stoneware. Umbers are powerful colorants, they have high iron and also contain manganese (the latter being the primary source of the color). ... more

Saturday 12th August 2017

Can you make a black-burning stoneware using black iron oxide?

Can you make a black-burning stoneware using black iron oxide?

Iron oxide has been added to a buff burning stoneware clay and samples fired at cone 6. They contain black iron oxide (10%, 5% and 2.5%). Even at 2.5% the raw pugged body is very black and messy to work with. Did they fire black? Or even dark grey? No. We have also tried 20% (mix of black and yellow ... more

Saturday 12th August 2017

This is how New Zealand kaolin powder agglomerates

This is how New Zealand kaolin powder agglomerates

These balls are easily broken down by the propeller in a slurry mixer. But they do not break down easily in a dry mixer, even when in a mix with other materials (like silica and feldspar). They just bounce around on a vibrating screen. That means that without some sort of finishing device in the dry ... more

Wednesday 9th August 2017

Dark Umber-Stained Engobes on M340 at cone 6

Dark Umber-Stained Engobes on M340 at cone 6

This is the standard Plainsman L3954D white engobe recipe with the 10% Zircopax switched for Raw Umber. The result is a very dark, rich, ultra-gloss brown (almost black). The engobe is applied inside and half-way down the outside. The mug on the left is glazed inside and out with the base GA6A ... more

Wednesday 9th August 2017

GA6A Alberta Slip base using Frit 3124, 3249 and 3195 on dark body

GA6A Alberta Slip base using Frit 3124, 3249 and 3195 on dark body

The body is dark brown burning Plainsman M390 (cone 6). The amber colored glaze is 80% Alberta Slip (raw:calcine mix) with 20% of each frit. The white engobe on the inside of two of the mugs is L3954A (those mugs are glazed inside using transparent G2926B). The Alberta Slip amber gloss glaze ... more

Tuesday 8th August 2017

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Interactive glaze chemistry calculations.


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• Thank u for your helping researchers .. Thank u for your efforts.

• 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.

• 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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• Your website has become an excellent resource for students and professionals alike, congratulations.

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