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Conquer the Glaze Dragon With Digitalfire INSIGHT Glaze Chemistry Software

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This software is focused on ceramic glaze chemistry calculations.

Download: Windows (2014-8c), OSX (2014-8c), Linux (2014-8c)


Test, Document, Learn, Repeat in your account at insight-live.com

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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. Search is coming soon.

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Pure cobalt carbonate and copper carbonate at 1850F

Cobalt carbonate (top) and copper carbonate (bottom). Left is the raw powder plastic-formed into a sample (with 2% veegum). Right: fired to 1850F. The CuCO3 is quickly densifying over the past 100 degrees and should begin to melt soon.

Tuesday 21st October 2014

Strontium carbonate self destructing

Strontium carbonate fired at 1800F and then allowed to rehydrate in the air for two days. It is crumbling like this all by itself, similar to what calcium carbonate does.

Monday 20th October 2014

How small can clay crystals be?

Table salt crystals on a 60 mesh screen. It has an opening of 250 micro meters (these are the half of the crystals that passed this size). Notice on the right, several crystals are in the openings, about to fall through. Imagine that bentonite or ball clay crystals can be 0.1 um in diameter, that is 2500 times smaller on a side. That would be 2500x2500 on a layer the size of a salt crystal and the thickness of a clay crystal. Since the clay crystal is much thinner than wide, perhaps ten could stack to the same dimension. That means theoretically 2500x2500x25000 could pack into a grain of salt!

Friday 17th October 2014

The way cones bend

An unfired cone (right) with others at various stages of bending. It can take 20 or 30 degrees to go from straight until bent as the first one. But the more a cone bends the faster it goes down (between the next two may only be 5 degrees). If the tip touches (as has happened with the front one) then it no longer indicates temperature change accurately. It is wise to have a cone in all glaze firings to verify the electronic readings.

Thursday 16th October 2014

Feldspars, the primary high temperature flux, melt less than you think.

A cone 8 comparative flow tests of Custer, G-200 and i-minerals high soda and high potassium feldspars. Notice how little the pure materials are moving (bottom), even though they are fired to cone 11. In addition, the sodium feldspar move better than the potassium ones. But feldspars do their real fluxing work when they can interact with other materials. Notice how well they flow with only 10% frit added (top), even though they are being fired three cones lower.

Tuesday 21st January 2014

Iron Red glazes look a little different in a flow tester

Melt flow test comparing two cone 6 iron red glazes fired to and cooled quickly from cone 6. Iron reds have very fluid melts and depend on this to develop the iron red crystals that impart the color. Needless to say, they also have high LOI that generates bubbles during melting, these disrupt the flow here.

Tuesday 23rd July 2013

Does Zircon only whiten and opacify a clear glaze? No.

This melt flow tester demonstrates how zircon opacifys but also stiffens a glaze melt at cone 6. Zircon also hardens many glazes, even if used in smaller amounts than will opacify.

Wednesday 18th February 2009

The the glaze laydown is not even, it could affect the fired surface

Dried glaze layer on a lightly grogged middle temperature stoneware (Plainsman M325). Notice how the bubbling that occurs during the drying of the glaze has disrupted the laydown. This is a glossy transparent and will likely level out, but if it were a matte or glaze having a stiffer melt, this texture would be evident in the fired piece.

Wednesday 15th October 2014

LOI in an all fritted glaze? Yes!

G1916Q and J low fire ultra-clear glazes (contain Ferro Frit 3195, 3110 and EPK) fired to 1650F. Notice how the volatiles from within the glaze itself are still burning after the glaze has melted. This glaze has lost 2% of its weight to this point. These products of decomposition need the right circumstances to clear or the glaze will have micro bubbles that cloud it.

Wednesday 15th October 2014

Is Lincoln 60 really a fireclay? Simple physical testing says...

Materials are not always what their name suggests. These are Lincoln Fireclay test bars fired from cone 6-11 oxidation and 10 reduction (top). The clay vitrifies progressively from cone 7 upward (3% porosity at cone 7 to 0.1% by cone 10 oxidation and reduction, bloating by cone 11). Is it is fireclay? No.

Friday 22nd August 2014

A completely automatic reduction gas kiln. This is heaven!

Blaauw kiln at the Potter's in Residence program at Medalta Historic site in Medicine Hat, Alberta. This type of kiln has an automatic controller that controls the firing schedule and atmosphere inside the kiln. These kilns are expensive, but bring the same degree of precision and convenience to reduction firing that electric kiln users have been enjoying for some time.

Wednesday 15th October 2014

What temperature do Orton cones actually go to in my kiln?

The blue line represents numbers from the Orton cone chart for 108F/hr. It is not as straight as what I expected. The red line is the temperature measurements that we have recorded after many test firings at each temperature. We use large cones in these firings and finish the firings manually to shut the kiln off just before the firing cone touches. These are now target temperatures that we use for automatically firing each temperature.

Tuesday 16th September 2014

What is sintering?

Bentonite fired to 1650F in a small crucible. Between 1600 and 1650 it is beginning to sinter (the particles are bonding, this is happening without any glass development). The powdered mass is beginning to behave as a unit, shrinking away from the walls.

Wednesday 15th October 2014

When crazing like this happens, it is a RED LIGHT. Pay Attention.

Crazing is a disaster for a production potter. Consider what one said: "I have just recently been contacted by a customer due to small lines in her bowl. I am now terrified residual crazing could be happening to lots of functional pieces I have sold! Nightmare! I have a terrible feeling in my stomach. Could anyone tell me if it is the glaze and if there is anything I can do to alter the recipe?"

Wednesday 15th October 2014

Terra cotta gets brittle when over fired

An excellent example that demonstrates the brittleness typical of vitrified terra cotta bodies. This bowl was fired to cone 02 and rung like a tuning fork when struck with a spoon. The body is dense like a porcelain and at appeared to be incredibly strong (this body is much more vitreous than an average terra cotta would be). However after a few more taps with the spoon it broke in two! It is brittle! Very hard, but brittle. At first I thought it might be that the glaze is under compression, but when I dropped the halves they did not shatter in the manner characteristic of compressed glaze, and they broke with razor sharp edges (like a vitrified porcelain does). So firing for this body must stop short of the most dense matrix possible to avoid this brittleness.

Wednesday 18th December 2013

Wow, what a surface. How?

A cone 10R sculpture clay containing 40% ball clay, 10% kaolin, 10% low fire redart (for color and maturity), some quartz and 25% 20x48 grog. This fine grained base produces a body that feels smoother than it really is and is very plastic. It is even throwable on the wheel.

Wednesday 28th November 2012

This cone 6 transparent looked good, but I still improved it alot

The green boxes show cone 6 Perkins Studio Clear (left) beside an adjustment to it that I am working on (right). I am logged in to my account at insight-live.com. In the recipe on the right, code-numbered G2926A, I am using the calculation tools it provides to substitute Frit 3134 for Gerstley Borate (while maintaining the oxide chemistry). A melt flow comparison of the two (bottom left) shows that the GB version has an amber coloration (from its iron) and that it flows a little more (it has already dripped off). The flow test on the upper left shows G2926A flowing beside PGF1 transparent (a tableware glaze used in industry). Its extra flow indicates that it is too fluid, it can accept some silica. This is very good news because the more silica any glaze can accept the harder, more stable and lower expansion it will be. You might be surprised how much it took, yet still melts to a crystal clear. See the article to find out.

Wednesday 19th February 2014

Why does the right glaze crawl and the left does not?

The glaze on the right is crawling at the inside corner. But two factors contribute. First, the angle between the wall and base is sharper than on the left, and a thicker layer of glaze has collected there (the thicker it is the more likely it is to crack on drying). In addition, the glaze on the right also shrinks more because it has a higher clay content.

Wednesday 25th July 2012

Why does the glaze on the right crawl?

This is G2415J Alberta Slip glaze on porcelain at cone 6. Why did the one on the right crawl? Left: thinnest application. Middle: thicker. Right thicker yet and crawling. All of these use a 50:50 calcine:raw mix of Alberta Slip in the recipe. While that appears fine for the two on the left, more calcine is needed to reduce shrinkage for the glaze on the right (perhaps 60:40 calcine:raw). This is a good demonstration of the need to adjust raw clay content for any glaze that tends to crack on drying. Albertaslip.com and Ravenscrag.com both have pages about how to calcine and calculate how much to use to tune the recipe to be perfect.

Thursday 1st August 2013

A good example of the superiority of a frit

Both of these glazes were made as 1000 gram batches and then mixed with the necessary amount of water to produce a slurry of the correct consistency. The one on the left is a fritted glaze with 20% kaolin, the one on the right is a Gerstley Borate based raw glaze (30% GB + feldspar, silica, ball clay). The GB glaze required much more water and gelled shortly after (it also tends to dry slowly and crack during drying on the ware). The fritted glaze has very good slurry and application properties.

Thursday 19th December 2013


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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