Click here for information about DIGITALFIRE Corporation

Contact Me

Let's have a together and answer your questions.

Other ways to Support My Work

Subscribe to Insight-Live.com. It is about DIY testing and development, not letting information slip away.

Help Me on Social

Tony Hansen
Follow me on

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

Login to your online account

Chemistry plus physics. Maintain your recipes, test results, firing schedules, pictures, materials, projects, etc. Access your data from any connected device. Import desktop Insight data (and of other products). Group accounts for industry and education. Private accounts for potters. Get started.

Conquer the Glaze Dragon With Digitalfire Reference info and software

Download for Mac, PC, Linux

Interactive glaze chemistry for the desktop. Free (no longer in development but still maintained, M1 Mac version now available). Download here or in the Files panel within your Insight-live.com account.


What people have said about Digitalfire

  • All your info on glaze chemistry and material characteristics are very informative and great catalysts for pushing me to take things a bit further. Most appreciated.
  • I Everyday visit your website http://digitalfire.com. Fantastic knowledge you have....thanks .
  • Keep up the fantastic work!
  • What a lovely surprise to find you online. As I've changed to Broadband you were allowed through and I'm really pleased. I'm quite sure your site will be a source of much inspiration.
  • Thank u for your helping researchers .. Thank u for your efforts.
  • Your work has been incredibly helpful. Magic of Fire especially.
  • Your information is very professional and I would like to incorporate in and on going education blinder for our community studio.
  • Ceramicmaterials.info is a fantastic resource!
  • I'm finding the magic of fire fantastic!
  • As I read this I am thinking wow, what a great article, so useful and I love the details of the pictures.

What people have said about Insight-Live

  • This article on porcelain is terriffic. I've been slip casting my own porcelain formula for nearly 40 years, and wish I had read it way back when I was first starting out! You provide exceedingly useful information- especially pertaining to the difficulties of trying to maintain consistency in a world of materials that are changing rapidly or disappearing entirely!
  • A short, but comprehensive description with lots of needful information like yours is rarely to be found in the internet. Bravo!
  • I have everything hand written in my notes from my glaze void, but obviously, is not searchable. It's great what you've done.
  • Thank you very much for publishing digitalfire.com - it's a wonderful resource and I've enormous respect for the enormous dedication you've put into it over the last 3 decades - thank you very much!
  • And I want to add - you are doing a magnificent job with your webpage. Just unbelievable amount of work and information you put there. I have learned a lot from your webpage. Thank you.
  • I wish to thank you for letting people like me use the information you have on the endless glaze articles you do, for free. Yes I am embarrassed not contributing but sadly currency exchange rates makes payment at the moment way out of my league. However, should you prefer I don't use your amazing site please let me know. Again my thanks for the glaze education I am getting from you.
  • I am a computer/tech guy and was drawn to your info because it is systematic, detailed and comprehensive. I started pottery and wheel throwing January 2018 on my 59th bday. I am ecstatic!
  • First, I love your site so much! Thank you for the countless hours that have been put into this!
  • I just wanted to express my appreciation for digital fire. It's an invaluable resource that I've been using since I was 18 years old (more than a decade). Keep up the amazing work.
  • I want to thank you for creating all that extensive and wonderful material in Digital Fire and Insight Live. I have started with the process of creating my own glazes a little bit more than a year ago, process that I found exciting and challenging and thanks to your websites it has been a lot easier!
June 2026: We are continuing a major code rewrite. Please contact us if you find issues. Thank you.

Monthly Tech-Tip from Tony Hansen

I will send practical posts like these (from thousands I maintain). No ads or tracking. The first email will provide one-click unsubscribe. Signup is being email-bombed by bots. For now, please subscribe inside your insight-live.com account.


Blog

Republishing of Digitalfire Content

I wish to express my gratitude to all the people and organizations around the world that have been republishing content on Digitalfire (most often with translation). They are mostly people who love ceramics and IT like me; mirror sites are developing on every continent. When people ask, I almost always agree; I feel gratitude that the pages are valued (so please don't hassle them for copyright infringement). Thank you messages, often emotional, arrive every day. They come from individuals, but also large corporations, schools, organizations and even high-tech industries. Some are amazing people who work in the background, the mainstream unaware of their brilliance. I've gotten thousands of cups of virtual coffee and countless donations in the past few years. It is a little overwhelming! Some very exciting liaisons are forming with republishers; you will see them as outgoing links and added functionality at digitalfire.com.

Context: Digitalfire Reference Library

Sunday 14th June 2026

Same body, same outside glaze.

But the inside transparent glaze is different

Glazing black clay bodies stained with manganese is just about impossible with typical transparent glazes. The glaze over-fluxes the clay surface and ruins the color. Worse, if it accelerates surface maturity, the body can blister or generate LOI gases that blister the glaze. How about transparent glazes over a black engobe instead? At least the body color is not lost. But the wrong transparent glaze can do what you see here (inside left).

These mugs are a buff stoneware, Plainsman M340. A black engobe was applied by pouring the inside and dipping the outside two-thirds of the way down.

Left: A L3954F black engobe was applied inside and upper exterior at leather hard. After firing to cone 6 using the PLC6DS schedule, G2926B—which is crystal clear on M340 itself—became completely clouded over the engobe because bubbles generated during firing remained trapped in the melt.

Right: The entire mug was dipped in GA6-B. The Alberta Slip particles and the melt characteristics of GA6-B promote bubble coalescence and escape, producing an exceptionally glossy jet-black surface over the same engobe.

Monday 8th June 2026

No glaze chemistry needed

At least not right away

You have 147 glaze recipes. How can you get your head around all of them? Is glaze chemistry needed? No, that's a "maybe" way in the future. Right now, you need to start organized documentation. The recipe for each. A few pictures of each fired on different clay bodies, different thicknesses. Perhaps slow and fast-cooled firing. This is what an account at Insight-live does well. What it does even better is tracking your testing. The first step is to assign each recipe a proper code number (replacing these) and write that on all test specimens and buckets. From this point on, learn. Record every observation you make about each in its notes.

Through all of this, constant use in the studio (or factory) will never stop surfacing problems (e.g. settling in the bucket, crazing, running, blistering, material issues, etc.). The seriousness of each will determine the level of attack. First, identify the mechanism of the desired fired result. If it is a base recipe plus additions of colorants, opacifiers or variegators, then check if the base of one of the other glazes has a similar surface texture and character. If so, then could the additives in the troublesome one be used with the better base? If not, then it's time to sanity check the recipe and bring out the heavy guns of at least looking at the chemistry. But in Insight-live, you only need to turn on the display of the unity formula (there is nothing else to do). Next, make sure each material in the recipe links to one in the material database (so the calculated formula is accurate). Then compare the calculated unity formula with a limit formula (often a simple sanity check, like with the recipe, quickly spots oxides that are in excess or are short.

Thursday 4th June 2026

A transparent glaze is going satin:

Is it the feldspar and kaolin substitutions?

A potter reports that a switch from G-200 feldspar to Mahavir, and EPK to Imerys kaolin, has resulted in this transparent glaze becoming more satin. Is that possible? Yes. Because this glaze is on a unity formula tipping point.

To see it, you do not need to know how to do glaze chemistry, just how to display the calculated unity formulas side-by-side. My Insight-live shows them here. The material change has little effect. But there is an anomaly: 0.29 MgO. That is magnesia matte territory. The MgO is very likely there to help bring the thermal expansion as low as possible (to avoid crazing). For people who cool their kilns relatively quickly, this fires glossy. But a material change could well affect the cooling rate needed to maintain the gloss. That being said, the potter may also be firing slower, yet attributing the mattness to the materials. Or it could be a combination of both.

This is a popular glaze, among others in the book "Mastering Glazes". In Ron Roy's circumstances, and for many others, it is glossy. But for this potter, a small change (in the recipe materials and also likely in firing) has produced this issue.

Context: MGBase3, Tipping point

Thursday 4th June 2026

Alberta Slip as a functional honey-transparent base:

The glaze I reach for again and again

The functional surfaces on these pieces all employ the GA6-B base honey glaze recipe. On Plainsman native stoneware clays, especially darker burning ones, typical transparents are very prone to micro-bubble and clouding issues. But not this glaze. The likely reason is that Alberta Slip contains coarser particles (it is only processed to 42 mesh), these act as a fining agent.

This glaze brings multiple other benefits:
-It fits Plainsman bodies, all of them.
-It is made from materials mined in Canada.
-The Alberta Slip base produces a thixotropic slurry.
-It acts as a very good base for dark colors and black.

The top mugs are GA6-B inside and out (MNS clay body). The top right has a black engobe under it.
Bottom left: GA6-B inside, GA6-C outside (MNS and Coffee Clay)
Bottom right: L4768E Coffee casting and M340 casting.

Context: I drink from these.., This GA6-B glaze is..

Thursday 4th June 2026

Are glazes food safe just because they carry a label?

This Gemini-generated mug could conceivably exist yet carry these labels. Yet experienced ceramic technicians would immediately be suspicious. The glaze is highly fluid and heavily crystallized; both suggest low or very low Al2O3 levels (it is the key oxide that makes glazes durable). If the interior color were produced using a cadmium-containing encapsulated stain, cadmium-release testing would be essential before claiming the ware is food safe. This is clearly engineered for visual effects rather than durability. None of those characteristics prove it is unsafe, but they do mean that labels like "nontoxic" are not substitutes for actual leach testing. A glaze can be made entirely from materials classified as nontoxic and still fail to meet the durability standards expected of functional foodware.

Context: Commercial glazes on decorative.., ASTM D-4236 - Standard..

Thursday 4th June 2026

Should I glaze the outside of this mug now? No!

This bisque mug has been glazed on the inside. But the bisque has absorbed water from that glaze, and this thin-walled mug is now waterlogged as a result (except at the thicker base). It does not have the absorbency needed to build up a thick enough layer of glaze on the outside. Even if it did, the water from the two glazes would wet the bisque so much that its drying time would be greatly extended. This is a problem because the mechanism of attachment of glaze to the body is fragile and works best when the glaze dries quickly. When drying is too very slow, bubbling and cracking often occur (leading to crawling in the firing).

Context: Does bisque ware need.., Glaze thickness

Monday 1st June 2026

Yixing teapot making. Is it magic?

Or highly evolved craft and science?

The Yixing teapot craftsmen appear to break all the rules and yet produce impossibly delicate and symmetrical pieces. Hao-Tong Yan, one of those craftsmen, and I have been trying to understand the technical reasons for how this amazing craft is possible. It turns out not to be magic, but actually a highly evolved understanding of a very unusual material. Here are some of the things that we are coming to understand (which is making it possible to create a facsimile of the clay in North America).

-The Yixing ore can have the appearance of being like rocks, yet they make a workable clay body from it.
-The clay appears highly plastic yet is not; the workability is coming from surprising places.
-The clay is stiff enough to resist deformation, yet is cohesive enough to join seamlessly.
-Craftsmen flatten the clay with a mallet, instead of rolling it, yet it does not stick to the board.
-Sections are simply glued with slip, yet they hold.
-The clay burnishes, yet is not smooth.
-Fired ware is smooth, yet the soft clay appears sandy.
-The fired surface is glossy, yet there is no glaze.
-The fired clay appears super dense yet does have porosity.

Context: Yixing Clay Teapots on.., Stunning video of Yixing..

Saturday 30th May 2026

2026: ChatGPT is doing credible troubleshooting

I uploaded a screenshot of this recipe panel from Insight-live and asked ChatGPT why sanitaryware using this glaze is dunting. Its response is impressive, good enough to provide remediation ideas.

-It notes things about the recipe that are unusual. For example, that the Al2O3 of 0.69 and Si:Al only 4:1, plus 13% calcined alumina, make this glaze more like a refractory enamel than a normal glaze.
-Its observation that crystallization could mean the real thermal expansion may be different from the calculated one, maybe much lower.
-Barium carbonate decomposition does not seem like something that would contribute to dunting, but its presence is strange for such a glaze.

Based on its answer, I think the 13% calcined alumina is the wild card, which is way too much for any glaze to dissolve, something to deal with first.

Context: ChatGPT was completely wrong.., ChatGPT is surprisingly wrong.., Two ChatBots square off.., Does ChatGPT know the.., Sanitary ware

Tuesday 26th May 2026

Crystalline glazes normally craze:

Here is one way to fix that

The mug on the left, made by Holly McKeen, is a typical cone 10 Grolleg kaolin mullite porcelain (highly vitrified, low in residual quartz). Its glaze is crazed. Crystalline glazes are high in Na2O, making crazing virtually certain. Since most pieces are decorative, crystal glazers just accept this as part of the process. But these are functional mugs, the glaze needs to fit (if only for ware strength).

But what if the thermal expansion of the body could be significantly raised? The body on the right is Crystal Ice, it contains 40% silica (vs 20-25% in a typical porcelain). The percentage of Nepheline has been reduced, lowering vitrification to about 1.5% porosity. As a result, more quartz survives undissolved and less mullite develops, raising the body’s thermal expansion. The result is a body with a much higher thermal expansion, so it can not only relieve the glaze tension but actually put a squeeze on it. There is a downside: These are less resistant to dunting and thermal shock failure during use.

Could the glaze be adjusted instead? Yes. Some of the Na2O could be substituted for Li2O, the latter is also a strong melter but has a much lower thermal expansion. Glaze chemistry could be used to source it from Spodumene (to avoid solubility issues with lithium carbonate). However, zinc-silicate crystalline glazes are very sensitive systems, so the more lithia is introduced the more likely the effect on the firing window, crystal size/density and background clarity.

Context: Crystalline glazes, Calculated Thermal Expansion

Tuesday 26th May 2026



https://digitalfire.com, All Rights Reserved
Privacy Policy

1