Click here for information about DIGITALFIRE Corporation

Melt fluidity and coverage: RedArt Slip vs. Albany Slip vs. Alberta Slip

Melt fluidity testers show similar flow but the amber clear glaze on the mugs shows some differences

These three melt flows and mugs were fired at cone 6 (using the C6DHSC firing schedule). The benchmark recipe is 80% clay and 20% Ferro Frit 3195. The center melt flow and mug (made from a Plainsman 3D-based stoneware) employs original Albany Slip as the clay portion. The one on the far left uses an Albany Slip substitute that was developed by calculating a mix of RedArt and other materials to have the same chemistry as Albany Slip. The one on the right employs Alberta Slip. Notice that, although the Alberta Slip version has a very similar melt flow, on the mug it is apparent that it needs a little iron oxide for a better match (e.g. 1-2%). And the glaze on the left: The chemistry of RedArt is different enough from Albany that some compromises in chemistry-matching were needed to avoid over-supplying the iron even more (and firing even darker than this). Although this Redart version runs in a very similar pattern on the melt flow, the character of the glaze is somewhat different on the mug (a better match can be achieved by increasing the frit percentage slightly, or firing to cone 7).

Context: Albany Slip, Redart, Alberta Slip, Ferro Frit 3195

Friday 10th July 2020

Ferro lead alumina bisilicate Frit 3602 melt flow over many temperatures

A 9 gram ball of frit melts and flows downward more and more as temperature increases.

This demonstrates the amazing melt behaviour of lead-as-a-flux for ceramic glazes. Not only does it melt early, but it softens slowly over a 300F range of temperatures before it goes off the end of the runway on this GLFL test. Then, when fired 200F hotter than that, it remains a stable, clear and uncrazed glass. Beginning around 1750F, this becomes a transparent glaze, by itself.

Context: Ferro Frit 3602, Lead Bisilicate Frit, 1700F Frit Melt-Off: Who is the winner?, Is Mexican Terra-cotta pottery lead-glazed? Yes., Lead in Ceramic Glazes

Thursday 9th July 2020

1700F Frit Melt-Off: Who is the winner?

Melted balls of 15 frits on a ceramic tile

These were 10g balls melted using our GBMF test. Frit 3602 is lead bisilicate. But it got "smoked" by the Fusion FZ-16 high-zinc, high-boron zero-alumina! Maybe you always thought lead was the best melter. That it produced the most transparent, crystal clear glass. But that is not what we see here. See something else? Each frit has a melt-fingerprint. Two are similar, it is immediately evident which.

Context: Fusion Frit FZ-16, Ferro Frit 3602, Glaze Melt Fluidity - Ball Test, Fusion Frit FZ-16-2 melt flow over many temperatures, Ferro lead alumina bisilicate Frit 3602 melt flow over many temperatures

Thursday 9th July 2020

Imagine if you had everything for production at home during Covid-19

All the things a potter needs: materials, equipment, supplies, tools

This is what you need to be independent, to create your own manufacturing company in your garage. Some of the prices are "instead of" rather than additive. There are many approaches to glazes, the more you are willing to learn the better you will be able to make your own (and save a lot). We recommend the cone 6 range using a small test kiln (like this 220v ConeArt GX119, don't scrimp on this, go for quality and the practicality of a Genesis controller). A kiln you can fire often and inexpensively is a key enabler to learning, developing techniques, products, designs, durable and decorative surfaces, solving problems. It can be fired multiple times a day. And it is big enough for mugs and similar sizes. It will get you into the habit of using some of your creativity for experimenting. It will give you the successes early on that will inspire you to press on learning. When you are ready, then get a big kiln and hit-the-ground-running. This potter's wheel is the best available and will last a lifetime, these often appreciate in value over time. And, build yourself a good plaster table. You will use it constantly. Not shown here is a propeller mixer, also an important tool. And you will need a sink equipped with a sink trap (Gleco Trap).

Context: Where Do I Start?, Trafficking in Glaze Recipes, Propeller Mixer, Test Kiln

Monday 6th July 2020

Is Mexican Terra-cotta pottery lead-glazed? Yes.

A lead-glazed handled cup still common sold in markets in Mexico

This piece was bought in Sinaloa in 2020. The merchant said it was made in Puebla. The lead test procedure involves leaving white vinegar in the piece overnight, pouring some of that into a test tube, dipping a cotton swab into a reagent solution and then stirring the vinegar. The color indicates lead content. As you can see, it has turned black, indicating heavy concentration of lead. This pottery is a tradition in Mexican culture and is used for food and liquid surfaces everywhere. There are manufacturers trying to make stoneware that retains the traditional appearance, but few people use it. Further refiring tests demonstrated that these are fired around 1700-1750F, a temperature sufficient to melt pure lead bisilicate into a glossy transparent but the body is still very soft and porous.

Context: Ferro lead alumina bisilicate Frit 3602 melt flow over many temperatures, Refiring a terra cotta piece has darkened the color, Lead Toxicology

Saturday 4th July 2020

The ball clay you use to suspend your glaze is important!

I poured 4 teaspoons of two glazes onto a non-absorbent butcher’s board and let them sit for a minute, then inclined the board. The one on the right employs Gleason Ball clay, the left one has Old Hickory #5 ball clay. Neither has any slurry property modifier addition. The one on the right has settled and on incline the watery upper is running off. The other has gelled and the whole thing is running downward slowly. Below I have begun to sponge them off, the one on the right is sticky. The most amazing thing about this: This difference appears despite that there is only 7% ball clay in the recipe.

Context: No. 5 Ball Clay, No. 1 Glaze Ball Clay, Ball Clay, Suspension, Glaze Slurry is Difficult to Use or Settling

Friday 3rd July 2020

Fusion Frit FZ-16-2 melt flow over many temperatures

This melt flow tester demonstrates the beautiful crystal-clear glass this zinc frit creates by 1700F. It fits this porcelain without crazing, even though very thick and high in sodium (the high zinc and boron are countering it to keep the thermal expansion down). It runs off the end of the runway around 1600F on this GLFL test, rivaling lead bisilicate. This is a more concentrated boron source than even Gerstley Borate. Everything about this material screams “ultra gloss”, what a material to build a fluid-melt reactive super-glaze on!

Context: Fusion Frit FZ-16, 1700F Frit Melt-Off: Who is the winner?

Friday 3rd July 2020

Form a ceramic glaze into balls? Why would you want to do that?

The process of dewatering a glaze slurry and making balls

The vast majority of glazes are plastic (but less than clay bodies). They can be dewatered on a plaster surface and formed. Why do this? To make 9-10 gram balls and fire them on flat tiles (or inclined flow testers) to see their melting characteristics. It is surprising how much this can tell you about the glaze. To make the ball, mix the slurry well and pour a little on the plaster. It should dewater in less than 30 seconds. As soon as the water sheen is gone, scrape it up with a rubber rib, hand-knead it and flatten it back down to dry a little more if needed (leave it only for five or ten seconds and rework it. Repeat until it is stiff enough to form balls of about 12 grams. Stamp them with ID numbers and dry them.

Context: Glaze Melt Fluidity - Ball Test, A Low Cost Tester of Glaze Melt Fluidity

Thursday 2nd July 2020

Lincoln Fireclay is plastic, it can be thrown on a potters wheel

Two freshly thrown mugs made from pure Lincoln 60 fireclay

The left two were made from a 100% mix of Lincoln 60, the right one adds 2% bentonite (Lincoln 60, by itself, matures into a stoneware at around cone 8). While it was possible to throw the pure material, the plasticity is a little lower than a normal pottery clay. That being said, it is smooth and has a soapy feel that makes it very pleasant to work with. A simple 2% addition of bentonite transformed it into a delight to throw! That only increased the drying shrinkage by about 0.5%.

Context: Lincoln 60 Fireclay

Thursday 2nd July 2020

Cone 1-4 stoneware by mixing a low and medium temperature body

Four tiles of a red-burning clay covered with purple, yellow, orange, black glazes

These tiles are a 50:50 mix of Plainsman L215 and M390. They are fired at cone 1, 2.5 &4 (columns 1,2,3). The glaze is G3806N (v1) with stains at 10% concentrations. That glaze is a fluid-melt for cone 6, but it performs nicely down to cone 1 and even lower. There is no visible crazing and the iron body is stoneware-strength. The firings were only held for 10 minutes at cone (no slow cool). These coloured glazes are also less "muddied" by the iron in the body than would be the case at cone 6. This is a really amazing result. Red-burning bodies can be difficult at cone 6 (if fired too high the red color is lost, if fired too low they are too porous).

Wednesday 1st July 2020

Contact Us:

Use the contact pages within or outside your account at Insight-Live.com


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

Login to your online account

Chemistry plus physics. The on-line successor to desktop Insight. Get an account for as little as $15. It does so much more.

Maintain your recipes, test results, firing schedules, pictures, materials, projects, etc. Organizing that data will better empower you to adjust, formulate and fix your recipes and processes. Link, share and publish.

Conquer the Glaze Dragon With Digitalfire Reference info and software

Still available for Mac, PC, Linux

Interactive glaze chemistry calculations. Free and unrestricted (legacy, no longer in development).


What people have said about Digitalfire

  • '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!"
  • I'm still reading about expansion and some of what you explained to me is in this article by digital ... so much lay men terms and analogies makes its more viewable to the mind and understandable... thanks - I continue to say thanks... Tony.... :)
  • I must say I am amazed by what I saw here. I am even more surprised to see so much of cermaic material stuff here.
  • Tony's site is really full of exceptional technical information.
  • I've become fascinated with Glaze chemistry in the last year or so, have purchased your book, and refer to your site from time to time as well...What a great resource! I have read your book a couple of times, but have not completely digested all of it. I suspect it takes most folks quite a bit of time!
  • After a lot of testing of various glazes I've decided he's overdue for sainthood.
  • I'll be reading and studying for a while, but what is so great is that the information is now right at my finger tips anytime that I need it - its all so very interesting - I never thought that chemistry would ever be interesting, - and I know now very soon I too will be able to slay the glaze dragon!

What people have said about Insight-Live

  • Absolutely love the insight-live web app.
  • How amazing it is to have personal contact on such an amazing technical site and I can’t express my gratitude for your generous spirit.
  • First i'd love to thank you for all the info you provide on digitalfire. it is an absolutely amazing resource and the way that you explain glaze chemistry/reactions has really helped expand my practice...I crave understanding and wisdom.
  • Your site is amazing and your videos too. Such an inspiration.
  • I discovered your website after trial and failure for 35 years. WOW ! The questions you have answered for me and the knowledge are immeasurable To think I am going to get past the Science and onto the Art makes me near giddy. Your site is amazing. My college age kids are going to be dazzled I did this. Every single college ceramic studio should know about your site. I want to tell them!
  • I write to appreciate your good works by way of the articles you made available on the net .. Thanks a million for your good work. From Nigeria.
  • Love the post (about leaching in glazes). I am the bad guy on Facebook ceramic because I always bring up this subject. So sad.

DigitalFire Logo

Privacy Policyhi11