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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

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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

  • I want to say THANK YOU! THANK YOU! for writing this book. It is exactly what I was looking for! I studied at a 4 year institutions--7 semesters in the ceramics department and I was taught how to calculate glazes with the empirical formula but that was it--no expansion stuff, etc. I wanted more than anything to have a knowledge base to create safe glazes, resolve problems like crazing, and the list goes on. In reviewing parts of your book many of my questions have already been answered. I absolutely love the way you address crazing--and yes, I did try many of the suggestions that were in that CM article and they didn't work. Now I know why. I have a lot to learn but am elated with what I have learned so far.
  • I have never understood the chemistry part of clay and glazes, so what you have done is great for me ... Your site is remarkable, but truthfully, I am just beginning to grasp parts if it.
  • First I'd like to thank you about your site. It's outstanding site.
  • I have been browsing the ceramic materials site with some of the Bastarache articles and their links. Extremely helpful information. Thank you both you and Edouard!
  • Am finding your website a treasure trove of extremely thoughtful writings for the aspiring more-technical studio potter. Thanks for putting it out there.
  • Thanks a lot for this sea of knowledge.
  • I'm trying to access a great article on deflocculation. I have formulated so many casting slips over the years with the help of what I learned in that article and on this site.
  • Where have I been. I could have used this site about a thousand times and would have saved myself about a thousand hours over the past years had I been aware of the remarkable information provided here.
  • I am impressed with your site - it is very comprehensive.
  • 'we have been using the arabia blue and white variation of the 5X20 cone 6 glaze, and have had a great response from our customers. Thanks for your efforts - you have made a believer out of me!"

What people have said about Insight-Live

  • Insight has become an important part of the ceramic industry for some time; this is my opportunity to express my gratitude. All I can say is bravo, and carry on.
  • You have such a brilliant analytical mind, able to find solutions to many ceramic problems. You have accomplished so much in your life, helping us potters understand what we are doing. I cannot thank you enough for your vast ceramic reference library online. I think you are a national treasure.
  • I am a high school senior AP ceramics student investigating glaze chemistry and rheology. I spend a great deal of my free time browsing the digitalfire reference library, and would have never developed the passion I have for ceramics chemistry had I not come across it.
  • Love the post (about leaching in glazes). I am the bad guy on Facebook ceramic because I always bring up this subject. So sad.
  • I love insight BTW. I have been showing everyone at Alfred how easy it is to do UMF while comparing two recipes next to each other. The up and down toggles make it easy to understand cause and effect. They are also impressed how easily i can switch between my computer and smartphone and maintain all my work and recipes. BTW I just love insight. It has changed my experience and knowledge of glazes drastically.
  • Digitalfire is just jaw-droppingly awesome. Thanks for all your hard work.
  • I just wanted to say, thank you! I’m relatively new to pottery, taking a mostly self-taught approach and I’m at the stage where glazing is in my mind. I don’t want to be (and can’t see myself ever) buying glazes from commercial suppliers. I want to learn my craft with glaze as much as I do with my clay preparation and pottery making. I’ve seen “the dragon” and been uninspired by so much of what I find online and to be honest, in many glaze books. It seems more popular to try and present a mass of glaze possibilities than to offer a learning experience beyond being told a glaze needs a melter, a refractory and a glass-maker. Enough to offer a very basic understanding, but nothing upon which to build the understanding that will allow some degree of mastery (or at least influence) of your glaze making. I am so pleased to have found digitalfire.com. You’ve shown me exactly how to approach and understand glazing, giving me the foundation for approach I sought. I was thinking of base glazes and what you’ve shown me about working on from those is fantastic and exactly what I was looking for. To have a reliable base glaze to modify and develop to meet different needs; to understand how to shift a melting point or adjust the surface gloss; to come to know how the mechanisms in a glaze and understanding them gives me the route to creating glazes that realize my intentions - wow! I can’t thank you enough. Rather than having to form a dumb reliance on a book of recipe cards and a bunch of website bookmarks (which I wasn’t wanting to go for) you’ve given me the foundation for a lifelong development and understanding of the glazes I will make, that will become “my” glazes. You have really opened my mind to the whole subject and it doesn’t seem to be a problem that I’m no scientist or chemist. You’ve shared your knowledge in a way that is completely approachable and remarkably easy to understand for someone without any kind of science/chemistry background.
  • Most people would lose the ability to troubleshoot how to problem-solve issues with Plainsman Clays without your documentation.
  • I am a ceramic manufacturing manager, and before this position, I had no training on ceramics. I was taught our recipes, but none of it was explained. The dragon ran amok. After reading through your articles and descriptions, I feel I have learned so much about my own products, and I have a foundation for changing, improving, and troubleshooting my materials issues that I wouldn't have had otherwise. They taught us in engineering school that we all stand on the shoulders of giants, because we all get to use knowledge and tools at a moment's notice that took others years to develop. Thank you for sharing all that you have, so the rest of us can stand on your shoulders to do our work that much better.
  • First, thank you for your site. I am approaching the subject from a more technical side of things rather than decorative or functional pottery but I have found the knowledge you share to be some of the most practical and useful information I have seen anywhere.

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Blog

People keep warning me about doing this...

But it has worked well so far.

When we finally hit an iceberg, perhaps the big question should be: "How did we get away with doing that for so long?"

Tipping point glaze recipes and practices are like this. I want to use those reactive glazes, so I need them to work. A quick test or two confirms what I want to see. That's the visible part of the recipe iceberg. But below the waterline is all that pesky recipe logic, material sense and glaze chemistry that bring up questions about the recipe before I even try it. And the trigger-happy glaze nerds who raise alarm bells about safety about glazes even though they have never actually mixed them up. I don't really want to hear about those things; I just want to double or triple layer those colorful runny glazes that look so nice on that social media post.

Context: Book Understanding Problems in.., Tipping point

Monday 19th October 2026

LOI horse race with a surprising winner and loser

A chart showing weight-loss vs firing temperature for common ceramic materials

This chart compares the decompositional off-gassing (% weight Loss on Ignition) behavior of six glaze materials (there are many more). Each was heated through the range 500-1700F at 350F/hr. It is amazing how much weight some can lose on firing. For example, 100 grams of calcium carbonate generates 44 grams of CO2! Magnesium carbonate even more. But the main message of this chart is that some late gassers overlap early melters. That can be a problem (causing glaze bubbles, blisters, pinholes). The talc in this test is an example: It did not finish gassing until 1650F. Yet many fritted and Gerstley Borate glazes have already begun melting by then.

There are two takeaways here. The biggest weight loser is not the biggest troublemaker. What matters is how gas release overlaps glaze sealing. Calcium carbonate illustrates this; its high carbonate content can still produce a clear glaze (when gases can clear ahead of any melting). And the talc, although having a small LOI, is a potential troublemaker when the glaze melt cannot effectively clear the bubbles.

Context: Light Magnesium Carbonate, Frit, Talc, Gerstley Borate, Calcium Carbonate, Dolomite, Ferro Frit 3124, LOI, Firing What Happens to.., Talc was making this.., Pinholing, Glaze Bubbles, LOI, Gerstley Borate stops gassing.., Comparison of frit melts.., Common frits begin melting.., Decarbonation, Talc has finished gassing.., Calcium carbonate talc finished.., Glaze Blisters

Sunday 18th October 2026

A wollastonite glaze slurry has agglomerates:

Is sieving the solution? Not necessarily.

This glaze has just been applied to a bisque tile. It contains wollastonite, a curious mineral because it has a shelf life (it can agglomerate in storage as a powder). Surprisingly, it can also form them in slurries. Other materials can also agglomerate; these include barium carbonate, iron oxide, cobalt oxide, clays, tin oxide, zircon and titanium dioxide.

This glaze was propeller-mixed, but that was not enough to break down the white lumps. Is sieving the answer? Maybe not. While screening can reduce the size of the lumps, it does not prevent their regrowth in the slurry (because smaller agglomerates that survive sieving can become starting points for larger clusters). A better option is blender-mixing. When that is done and re-agglomeration occurs, then the problem is more complicated.

Context: Wollastonite, Sieve, Agglomeration

Saturday 17th October 2026

EPK VS Grolleg in a transparent glaze:

Grolleg can also create an easy-to-use slurry

Yes. The two glaze cones are both the same Grolleg-based porcelains. Both of them have the same base glaze: 1947U transparent. But the one on the left uses EP kaolin, and the one on the right uses Grolleg kaolin. The Grolleg glaze has a dramatically cleaner appearance. The Grolleg does not suspend the slurry quite as well as EPK; however, it responds to gelling better (using vinegar or Epsom Salts, for example). This ability to facilitate an easy-to-use thixotropic slurry more than compensates.

Context: Grolleg Kaolin, G1947U

Friday 16th October 2026

2026 Great Plaster Squeeze Continues:

A crisis in North American ceramics

USG specialty plaster is entering a final-inventory phase in the ceramic supply chain, and rationing has begun at some suppliers even though the Southard plant does not close until November.

Oct 12: Arcosa appears to be ramping up to produce their equivalent to USG No. 1 . Arcosa Pottery Plaster consistency and strength make it a credible No. 1 replacement. The higher published maximum expansion could matter for dimensionally controlled molds, jigger tooling and multi-part mold registration. The data sheet does not quantify absorption rate, saturation behavior or expected casting turns, so equivalence is not yet established.
Oct 10: Industrial plaster shortages now reported beyond ceramics . A significant new industry report strengthens the evidence that North America's specialty-plaster supply chain is already struggling to absorb the impending closure of USG's Southard operation.
Sept 21: Industrial supplier freemansupply.com posts USG closure notices They state: "With the upcoming closure of U.S. Gypsum (USG), Freeman's plaster and cement supplier, we have been sourcing alternatives to continue supplying the industry with quality products. If you are interested in plaster or cement, please complete this form to be contacted when suitable alternatives are available".
Sept 17: GP requiring full load orders, actively staffing A distributor reports that GP is requiring no mixing of types on orders. GP is recruiting production at the Blue Rapids, Kansas facility specifically for continuous manufacturing of plaster products. 12-hour shifts, including weekends, holidays, and overtime.
Sept 14: Arcosa emerges as another replacement source Brackers Good Earth Clays says it has opened an account with Arcosa Specialty Materials and placed its first truckload order for pottery plaster plus a product comparable to Hydrocal White, due to arrive in October
Sept 9: Various distributors have no K-59 in stock The persistent K-59 shortages at ceramic suppliers suggest that distribution or production is not yet keeping pace with the emerging ceramic-market shift.
Sept 6: USG online store has an “LIMITED INVENTORY” notice It states that availability of USG plasters and gypsum cements is limited and that once a product sells out, it will no longer be available and will be discontinued. Interestingly, significant final inventory remains: 312 bags of No. 1 Pottery Plaster, 218 Hydro-Stone, 123 Ultracal 30 and 95 Hydrocal White, all in 47.5-lb bags. These are being offered for sale while supplies last. The main USG website and CGC pages still have ordinary-looking product listings for No. 1 Pottery Plaster, Cerami-Cal and other products, without conspicuous discontinuation notices.
Sept 2: GP announces close of a plant Georgia-Pacific officially announced that it will permanently close its Tacoma, Washington gypsum plant, affecting 125 employees. GP says weak repair/remodel demand is the reason, and importantly says it expects to continue satisfying customer demand from its remaining facilities. The Tacoma operation is a gypsum-board plant, not the Blue Rapids industrial-plaster operation associated with K-59, so this does not indicate that K-59 production is being cut. But it does show GP is actively rationalizing its gypsum manufacturing network rather than broadly expanding it at this moment.
Sept 1: A distributor is out of USG products It reports that it is completely out of USG No. 1 Pottery Plaster, Hydro-Stone and 20 Minute Casting Plaster, with only a limited amount of Hydrocal White remaining.
Aug 31: GP K-59 sold out at some suppliers Several Canadian suppliers are already showing Georgia-Pacific K-59 as sold out. Another still has 10 of K-59 available, compared with 172 bags of USG No. 1 Pottery Plaster still in stock. That suggests demand may already be shifting toward K-59 faster than some distributors can replenish it.
A signal from Georgia-Pacific itself: Its Blue Rapids, Kansas Industrial Plasters facility, the plant historically associated with K-59, is actively hiring maintenance personnel, including for a rotating 12-hour schedule, with the job posting emphasizing equipment reliability, production optimization and operating performance. Georgia-Pacific’s official industrial-plaster site continues to present pottery plaster as a core business and says it supplies sanitaryware and dinnerware manufacturers and produces both alpha- and beta-gypsum plasters. I still find no announcement of a production increase, additional shifts, capacity expansion, new warehouses, or a specific commitment to replace USG’s Southard volume.
Aug 29: One supplier is imposing anti-hoarding restrictions It will serve normal requirements of existing customers, but will not sell plaster to new customers or permit purchases substantially above usual volumes. It is investigating alternative sources. Another is now limiting Hydro-Stone purchases to 100 lb per customer per week. USG and CGC themselves still have active product pages for No. 1 Pottery Plaster, Hydro-Stone and Ultracal 30, with no visible discontinuation notice, so their public website continues to lag what distributors are reporting.
Aug 19: News from Australia An Australian industrial supplier now states that USG is “phasing out its entire Industrial Products range” made at Southard, that USG has confirmed these products will not be manufactured at another site, and that USG is no longer accepting orders.

Context: USG No 1 Pottery.., GP K-59 Pottery Plaster.., The demise of USG..

Wednesday 14th October 2026

Thrown pieces of pure Grolleg and EPK:

This is how you compare plasticities

Mugs thrown from two pure kaolins

These have just been thrown on the wheel. I find it to be a foolproof method of comparing the plasticity of two clays. They were slurried up and dewatered to about the same moisture content and the same amount was thrown to compare the size achievable. While the Grolleg is stickier and dewaters a little slower, it is not as plastic as dark EPK (which itself is not that plastic compared to others). Curiously, New Zealand kaolin (halloysite) is quite a bit less plastic than the Grolleg but it responds to plasticity augmentation (in porcelain recipes) just as well as Grolleg (similar amounts of bentonite producing similar plasticities). And, bodies containing EPK also need about the same amount of bentonite to produce plasticity suitable for throwing large forms. So, the plasticity that a kaolin appears to have by itself is not completely indicative of what it will contribute to a body (if augmented with bentonite). The EPK used here is the darker and more plastic of the two varieties Plainsman receives.

Context: EP Kaolin, Grolleg Kaolin, New Zealand Halloysite, EPK fired bar top..

Wednesday 14th October 2026

Kaolin and ball clay:

Why the uncracked disk is not the whole story

Left: OptiKast, a coarse-particle kaolin intended for slip-casting. Right: Plainsman A2 ball clay. These DFAC test (drying performance) disks were dried with their centers covered, deliberately creating uneven drying. The exposed perimeter dries and stiffens first; the covered center dries and shrinks later. The resulting cracks reveal how each clay responds to that stress. OptiKast feels smoother, yet its individual clay particles are much coarser than those typical of ball clay. This kaolin has low drying shrinkage, so its disk remained intact. The ball clay shrinks more. As its center dried and tried to contract against the already stiff perimeter, stresses developed, splitting the disk and opening numerous cracks around the edge.

So why use ball clay? This particular kaolin has so little plasticity that even making this disk was difficult. And the dried disk is fragile. Yet it is very useful in casting bodies, where plasticity impedes permeability. Ball clays are highly plastic; high drying shrinkage comes with that. Adding some of this to poor-plasticity casting or forming bodies that can tolerate a darker fired color can transform them into ones that both form well and dry harder and stronger.

Context: Ball Clay, Kaolin, OptiKast Kaolin, Drying Factor, It dry shrinks much.., Ultimate Particles, Primary Clay, Casting Rate, Ball Clay, WKS

Tuesday 13th October 2026

Better records, more testing, faster progress

How I manage dozens of simultaneous projects

This two-inch stack of clay body and glaze mix tickets represents only about half of my testing over the past year. Along the way, I also added thousands of photos to my Insight-live.com account. Looking at this pile, I realized why I am testing more: Organized records make it easier to keep multiple projects moving. I can see what I have tried, compare results and pick up where I left off. Each test builds on earlier work, and that visible progress motivates me to keep going. If you want to do DIY glazes and bodies, this is the secret is good record-keeping.

Context: Setting up a Clay.., Is this your testing.., A code on every..

Saturday 10th October 2026

20x5 Cone 6 glossy black with GR6-H, GA6-F glazes over:

Crawling will happen unless mitigations are taken

The underglaze is the 20x5 cone 6 base transparent glaze (G1214M with 5% Mason 6666 black stain). Overglaze left: GR6-H Ravenscrag Oatmeal. Overglaze right: GA6-F Alberta Slip oatmeal. Both produce a pleasant silky matte texture. Double layering using typical dipping glazes is prone to crawling (because of shrinking and cracking during drying). By keeping layers fairly thin, it is possible to achieve success, but with glazes high in clay content (as these are), more is needed. A mix of raw and roasted Alberta and Ravenscrag Slips is the answer here. Start with a 50:50 ratio and adjust to establish a balance between drying hardness and drying shrinkage. For more assurance in production situations, mix the underlayer black as a base-coat dipping glaze.

There are enough variables that a record-keeping system is needed. Start now, and you won't regret it.

Context: G1214M, GR6-H, GA6-F, GR6-H Ravenscrag Oatmeal glaze.., Reactive Glazes, Glaze Layering

Thursday 8th October 2026

Video: Convert a glossy glaze to a calcia matte:

Ten minutes of glaze-chemistry adrenaline!

Watch the G1214Z video to see me convert the G1214M 20x5 cone 6 clear base into G1214Z cone 6 calcia matte using simple glaze chemistry and recipe logic. This first appeared in the Digitalfire desktop Insight instruction manual 30 years ago. It is an understatement to say that this process is interesting if you want to know more about glazes, their chemistry and recipe logic. Watch this video and see me adjust the recipe of my high-calcium transparent cone 6 glaze to convert it into a calcia matte. In an Insight-live.com account, the process is easy enough for anyone. We'll cut the Si:Al ratio, increase the CaO, maintain the thermal expansion for glaze fit and make the recipe shrinkage-adjustable using a mix of calcined kaolin and raw kaolin. We will even compare it with the High Calcium Semimatte from Mastering Glazes.

Context: G1214M, Calcia Matte, Converting G1214M Cone 6..

Tuesday 6th October 2026


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