Javascript must be enabled in the security or content
settings of your browser for this site to work properly

To learn more about cookies search for HTTP cookie at

Click here for information about DIGITALFIRE Corporation

Home | Products | Support | Education 
About | Privacy | Search | Reference Database | Log in 

Conquer the Glaze Dragon With Digitalfire INSIGHT Glaze Chemistry Software

Install it on your PC

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

Use it online

Nothing to download or install. Revolutionary!

Tony Hansen's Thousand-Post TimeLine

I am the creator of Digitalfire Insight, and 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.


Flawless Ravenscrag Slip based glazes on a cone 6 stoneware

Plainsman M340 with Ravenscrag clear (inside) and pink glazes at cone 6. These were fired in a larger electric kiln at a slower firing rate, so the glaze has no imperfections. This pink glaze has proven to be very reliable and attractive on many clay bodies.

Thursday 16th October 2014

Copper Carbonate is beginning to melt. When?

Copper carbonate is beginning to melt at 2000F (this same sample was fired to 1950F, while shrunk to less than half its size, it was not melting yet).

Thursday 30th October 2014

No crazing out of the kiln. So it is good. Right? Wrong!

The side of this white porcelain test mug is glazed with varying thicknesses of VC71 (a popular silky matte), then fired to cone 6. Out of the kiln there was no crazing, and it felt silky and wonderful. But a 300F/icewater test was done and then it was felt-pen marked and cleaned with acetone. This is what happened! This level of crazing is bad, the dense pattern indicates a very poor fit. Then why was it not crazed coming out of the kiln? The glaze is apparently elastic enough to handle the gradual cooling in the kiln. But what the kiln did not do, time certainly will. This recipe has 40% feldspar (a big high-expansion KNaO contributor), that much in a cone 6 glaze it a red flag to crazing. Coupled with that was low Al2O3 and SiO2, another tip-off.

Thursday 30th October 2014

What does it take to get a crystal-clear low fire transparent? A lot!

These three cups are glazed with G1916S at cone 03. The glaze is the most crystal clear achieved so far because it contains no gas producing materials (not even raw kaolin). It contains Ferro frits 3195 and 3110 plus 11 calcined kaolin and 3 VeeGum. Left is a low fire stoneware (L3685T), center is Plainsman L212 and right a vitreous terra cotta (L3724F). Fired at cone 03. Crystal clear, almost no bubbles compared to the kaolin-suspended version. These all survived a 300F/icewater test without crazing.

Thursday 30th October 2014

Why does the left glaze not cutlery mark when it is barely melting?

Left: VC71 cone 6 silky matte glaze. Right: An adjustment that adds boron melter and SiO2/Al2O3 (which preserving their ratio). The dramatic improvement in melting was unexpected. Even though B has the same Si:Al ratio, it is completely glossy. Why? A (left) is simply not melting completely, that is why it is silky matte (not a true matte). Yet A feels like a good silky matte and is resistant to cutlery marking. Why? Feel alone can be misleading. Cutlery marking usually happens with matte glazes or heavily opacified whites, this is neither, it is an under-fired glossy glaze, fired just high enough not to mark.

Thursday 30th October 2014

A matte that is matte because it is not melting completely

Left: This specimen of VC71 cone 6 matte glaze was felt-marked and cleaned with acetone. A closeup of the ink specks reveals they are held in micro-bubbles breaking at the surface. This specimen has also been thermally stressed in a 300F/icewater test (causing the crazing pattern, which curiously, only shows up on part of the surface). Right: An adjustment to VC71 that adds more boron and Al2O3/SiO2 (while preserving the Si:Al ratio). It is much glossier, confirming that, even though the VC71 matte surface feels functional to the touch, it is a product of improper melting.

Thursday 30th October 2014

Can you throw and form a pure kaolin? Yes, but ...

Small thrown bowl made from pure #6 Tile kaolin. It is fired to cone 6. This type of surface cracking happens during the firing, it is typical when trying to fire a pure kaolin (it needs a filler). While this specific kaolin throws well all by itself, most are far less plastic. Pure kaolins are also refractory, so the porosity of this piece is very high, completely impractical for functional ware (it needs a flux like feldspar).

Tuesday 21st October 2014

LOI profiles of more common glaze and body materials

These are pure samples (with 2% binder added) of (top left to bottom right) strontium carbonate, nepheline syenite, cobalt carbonate, manganese dioxide, bentonite (in bowl), 6 Tile kaolin, New Zealand kaolin and copper carbonate. I am firing them at 50F increments from 1500F and weighing to calculate loss on ignition for each. I want to find out at what temperature they are gassing (and potentially bubble-disrupting the glaze they are in or under). Notice how the copper is fuming and spitting black specks on the shelf, this happens right around 1500F. These stains on the shelf darkened considerably when the kiln was fired higher.

Thursday 9th October 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

Crazing is a RED LIGHT. Pay attention! Even if it is a well known recipe.

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?" Yet this is easy to fix.

Wednesday 15th October 2014

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. It is long past the fuming stage.

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 as it rehdrates.

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

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.

Sign In or Register

Is your glaze problem related to it's chemistry? Ask Us!

Email address




Enter this code

Prove you are human

What people say about

  • Your information is very professional and I would like to incorporate in and on going education blinder for our community studio.
  • Your website is phenomenal, I love it to get insight on different oxides. I helps me alot, even though we are pretty specialized.
Click here to see all 173

DigitalFire Logo

Suite 407, 1595 Southview Drive SE, Medicine Hat, AB T1B 0A1
Answering Machine: (406) 662-0136, FAX: (403) 527-7508
Privacy Policy

CCBot/2.0 ( (6)