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Tony Hansen's Thousand-Post TimeLine

I am the creator of Digitalfire Insight, Digitalfire.com and Insight-live.com. I have made hundreds of posts like these on my Facebook page and personal timeline. My posts are like no others, they help you understand your glazes and clay bodies, take control. They are also part of the Digitalfire Reference Database (referenced from one or more articles, glossary entries, materials, oxides, test procedures, etc). Visit and Like my page to get a notification each time I post.

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Pushing the limits of an encapsulated stain

Mason 6021 encapsulated stain in Plainsman M370 transparent fired at cone 6 on M370 (with second layer of two other colors). Notice the bubbling. This stain is rated to 2300F, it appears that even cone 6 is pushing its limits.

Friday 7th November 2014

Cone 03 stoneware. I am almost there!

Cone 03 white stoneware with red terra cotta ball-milled slip and transparent overglaze. These are eye-popping stunning. They are test L3685U (Ferro frit 3110, #6 tile kaolin, Silica), near the final mix for a white low fire stoneware. The G1916J glaze is super clear. Why? Two reasons. These were fired in a schedule designed to burn off the gases from the bentonite in the body before the glaze fuses (it soaks the kiln for 2 hours at 1400F). Terra cotta clays generate alot of gases at cone cone 03, but here the terra cotta is only a thin slip over the much cleaner burning white body.

Saturday 22nd November 2014

Cone 6 black with a second layer of oatmeal glaze

The underglaze is G1214M cone 6 black (adds 5% Mason 6666 black stain). Overglaze left: GR6-H Ravenscrag Oatmeal. Overglaze right: GA6-F Alberta Slip oatmeal. Both produce a very pleasant silky matte texture (the right being the best). Both layers are fairly thin. In production it would be best to spray the second layer, keeping it as thin as possible. It is also necessary to adjust the ratio of raw to calcined Alberta or Ravenscrag Slips to establish a balance between drying hardness but not too much drying shrinkage (and resultant cracking).

Friday 20th December 2013

When a rutile blue glaze no longer fires blue

Left: What GA6-C Alberta Slip rutile blue used to look like. Middle: When it started firing wrong, the color was almost completely lost. Right: The fix. The problem? We were adjusting firing schedules over time to find ways to reduce pinholing in other glazes and bodies, the focus was slowing the final stages of firing and soaking there. In those efforts the key firing phase that create this effect was lost: it happens many hundreds of degrees on the way down from cone 6. The key? A 30 minute soak after cooling 270F from cone 6, then 150F/hr drop to 1400F.

Friday 20th December 2013

A batch of fired clay test bars in the Plainsman Clays lab

A batch of fired test bars that have just been boiled and weighed, from these we get dry shrinkage, fired shrinkage and porosity. Each pile is a different mix, fired to various temperatures. Test runs are on the left, production runs on the right. Each bar is stamped with an ID and specimen number (the different specimens are the different temperatures) and the measurements have all be entered into our group account at insight-live.com. Now I have to take each pile and assess the results to make decisions on what to do next (documenting these in insight-live).

Friday 21st November 2014

The magic of a small barium carbonate addition to a clay body

Two bisqued terracotta mugs. The clay on the right has 0.35% added barium carbonate (it precipitates salts dissolved in the clay to prevent them coming to the surface with the water and being left there during drying). The process is called efflorescence and is the bane of the brick industry. The one on the left is the natural clay. The unsightly appearance is fingerprints from handling the piece in the leather-hard state, the salts have concentrated in these areas (the other piece was also handled, but has very little marking).

Thursday 2nd January 2014

The classic cone 6 floating blue? No, it is Alberta Slip blue.

Fairly close in appearance to the classic cone 6 floating blue recipe used across North America, this is a variation of the Alberta Slip Rutile Blue glaze (except this adds 1% tin oxide, 1% black copper oxide and 2% ceramic rutile, it is GA6-C1). Because of the melt fluidity, it thins on the edges of contours and breaks to the color of the underlying body. It looks best on dark bodies, but if thick it is OK on light ones also.

Tuesday 23rd July 2013

The whitest burning plasticizer we have seen

Bentone (A.K.A. Macaloid MA) is a very plastic highly refined hectorite clay. This specimen has been mixed as a slurry, then dewatered until plastic on a plaster slab (it is very resistant to giving up its water). The plastic material has a very high water content, is exceptionally sticky and took many days to dry from the plastic stage. It shrinks 30% or more from plastic to fired and burns pure white at cone 6 (it can withstand higher temperatures). It burns whiter than similar materials from other manufacturers.

Wednesday 12th November 2014

Tenmokus made from Alberta Slip and Ravenscrag Slip

GR10-K1 Cone 10R Ravenscrag Tenmoku (right) compared to Tenmoku made from Alberta Slip (left, it is 91% Alberta Slip with 5% added calcium carbonate and 2% iron oxide). Left is Plainsman P700 porcelain, right is H570. Tenmokus are popular for the way they break to a crystalline light brown on the edges of contours.

Tuesday 23rd July 2013

Turbo-charge plasticity using bentonite, hectorite, smectite.

These are porosity and fired shrinlage test bars, code numbered to have their data recorded in our group account at Insight-live.com. Plainsman P580 (top) has 35% ball clay and 17% American kaolin. H570 (below it) has 10% ball clay and 45% kaolin, so it burns whiter (but has a higher fired shrinkage). P700 (third down) has 50% Grolleg kaolin and no ball clay, it is the whitest and has even more fired shrinkage. Crysanthos porcelain (bottom, from China) also only employs kaolin, but at a much lower percentage, thus is has almost no plasticity (suitable for machine forming only). Do H570 and P700 sacrifice plasticity to be whiter? No, with added bentonite they have better plasticity than P580. Could that bottom one be super-charged? Yes, 3-4% VeeGum or Bentone (smectite, hectorite) would make it the most plastic of all of these (at a high cost of course).

Sunday 30th October 2011

An additive that will make a glaze crawl

Light magnesium carbonate has been added to a low temperature terra cotta white glaze (about 10%). It induces crawling. It also mattes the glaze because it sources MgO.

Wednesday 25th July 2012

Alberta Slip cone 6 base slow cooled

GA6-A Alberta Slip base glaze (80 Alberta Slip:20 Frit 3134) fired with Plainsman slow cool cone 6 firing schedule on Plainsman M390 iron red clay. If this is cooled at normal speed, it fires to a glossy clear amber glass with no crystals.

Wednesday 19th November 2014

Underglaze color mayhem!

Commercial underglaze colors fired at cone 5 in a flow tester. Underglazes blend stains with a host recipe that should fuse them enough to adhere well to the body (two of these have not even begun to do that). The blue, green and red are from one manufacturer. Stain powders have different melting temperatures, so underglaze formulators must treat each stain individually, customizing the underglaze recipe to its melting behavior. As you can see, they have failed to do that here, the pink one has shrunk to half its size and is about to melt (it needs less flux). The green one is only sintered (it needs more flux). The black underglaze (D) (from a second manufacturer) contains gassing materials, it has become an Aero chocolate bar and is about to race down the runway. The E black (a third manufacturer) has not even started to melt or even sinter. The blacks were plastic, the colored ones were not. I am confused. How could the glaze possibly stick well to the body with the green or unmelted black under it?

Wednesday 5th November 2014

Marbling using a translucent porcelain

A transparent glazed marbled bowl by Tony Hansen. It is a made from Plainsman Polar Ice (a New Zealand kaolin based porcelain) and fired to cone 6. 5% Mason 6306 teal blue stain was added to the clay, then this was wedged only a few times. The piece was thrown, then trimmed on the outside at the leather hard stage and sanded on the inside when dry.

Thursday 5th September 2013

Highly refined plasticizers after firing to cone 6

Veegum (left), Mineral Colloid and Gelwhite fired to cone 6 oxidation. The Veegum is dense and white, but not melting. The Mineral Colloid fires like a typical raw bentonite (dark brown, high soluble salts and beginning to melt). The Gelwhite is completely melted and foamed.

Friday 27th December 2013

M340 Transparent Liner with Mason stains

M340 Transparent Liner glaze fired at slightly lower than cone 6. Using these modest stain amounts the degree of melting of the glaze is not overly affected (these were balls, they flattened during firing). However as a glaze layer on a body, many of these will not be as dark as you see here.

Thursday 22nd May 2014

Some glazes look great on red clay and horrible on white

Alberta Slip cone 6 lithium brown (GA6-G1) on a red burning clay (left Plainsman M390) and buff burning (right M340). Obviously this looks better on the former where iron from the underlying body variegates the entire surface and bleeds through on contours where the glaze is thinner, creating a breaking effect.

Tuesday 11th November 2014

M390 Cone 6 red with added kyanite, grog

Samples fired to cone 6. Lower left: Plainsman M390. Upper left: M390 plus 12.5% 48 mesh kyanite (no visible effect on fired color or character). Upper right: M390 plus 12.5% Christie STKO 22S 40 mesh grog (strangely it fires a darker color and appears more vitreous and there is no soluble salts circle). Both grogs were wedged into the clay and did not stiffen it or affect plasticity much (in fact, both were easier to pull up during throwing). The percentage water content went from the 21% to 19% in both.

Monday 10th November 2014

What is sintering?

Bentonite fired to 19500F in a small crucible. It is sintering, the particles are bonding even though there is no glass development. The powdered mass is behaving as a unit, the cohesive forces holding it together are enough to shrink the entire mass away from the walls of the container. This sintering process continues slowly, beginning around 1650. Most raw bentonites, this is National Standard 200 mesh, have a fairly low melting point, this will begin to fuse soon.

Friday 22nd July 2011

Guess which mugs are made using an NZ kaolin?

The two mugs on the left: Traditional Grolleg porcelain using Nepheline and bentonite (fired to cone 10R). The right: Using New Zealand kaolin, Nepheline Syenite and VeeGum.

Friday 25th April 2014


These posts are actually pictures referenced on pages in The Digitalfire Reference Database, thousands of pages of explaining things you need to know to formulate, adjust and troubleshoot traditional ceramic bodies and glazes. It is organized as: Oxides, minerals, materials, recipes, articles, glossary, hazards, library, MDTs for INSIGHT, pictures, properties, firing schedules, significant temperatures, tests and troubleshooting. Level 2 desktop INSIGHT and Insight-Live both interact with it.

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