Click here for information about DIGITALFIRE Corporation

Monthly Tech-Tip from Tony Hansen

I will send practical posts like these (from thousands I have made). No ads or tracking. One-click unsubscribe. Answer to correspond with me. If you are already subscribed the email will confirm it.


Blog

An industry misdirected by chemical analyses

A material lab report showing chemical analysis

In response to a query about the suitability of a material for use in our porcelain bodies this company asked for our "index requirements". It turns out they are asking: "What should the chemical analysis of the material be?" This is indicative of thinking that chemistry determines the absolute fired properties of clay body materials. However the physical properties the material contributes to our recipe are more important (e.g. the plasticity, the drying performance, the fired shrinkage and density, the translucency and whiteness). The chemistry is indirectly related to some of these bulk product could never be ordered without getting a sample and doing the physical testing. There is an exception to this: You have experience with a material and an alternative of the same type is being recommended. There are some aspects of the chemistry that can be extrapolated to comparative firing performance (e.g. iron and titanium content relate to whiteness and translucency, flux content to fired maturity). However the chemistry information should be coupled with mineralogy, particle size data, plasticity and casting indicators, etc. Another factor is that chemical analysis data is not always absolute (two laboratories using different methodology will produce different results). In the end it is just better to do the physical testing!

Context: Physical Testing

Wednesday 22nd September 2021

Two awesome low fire transparent highly fritted glazes for pottery

Melt fluidity comparison of two clear glazes

These work well from cone 04 up, they are better than any commercial transparent we have used. And far better than glazes made using raw sources of boron (like ulexite, colemanite, Gerstley Borate). These glazes have lower thermal expansion and do not craze on any body we have tried (yet are ultra gloss and ultra clear). They are G1916QL1 and G3879C. We developed them for use on the dolomite-based (rather than talc-based) L4410L low temperature art clay body. These are a good demonstration of the technical and economic sense it makes to use highly fritted glazes at low temperatures. Having a good base glaze is the key to adopting low temperatures for your production. You would likely agree that no stoneware glaze has melting patterns like these shown in this melt fluidity test! These recipes and all details about their development and adjustment are openly available.

Context: Transparent Glazes

Thursday 16th September 2021

What did I do to make this glaze stop crawling?

This opacified cone 6 glaze was crawling on this stoneware casting body. I thought it was because of

This is G2934Y white (with 10% Zircopax). I was blaming the zircon for the crawling. But, since the slurry had settled somewhat I was able to remove about 15% of the water and replace it with CMC gum solution. This gum addition was not enough to slow down the drying much (a reason that I avoid gum if possible). That fixed it! Meaning that adherence of the dried layer to the bisque was the issue. This being said, there were still a couple of small spots where it crawled. So I will replace another 5% of the water the next time I use it.

Context: CMC Gum, Crawling

Thursday 16th September 2021

Are you using your expensive kiln like a pop-up toaster?

A small controller-equipment kiln and views of programming it

Put the pots in, select a cone, press start. It is time to rethink that approach! Seriously. The Bartlett Genesis kiln controller is standard equipment on hobby and production electric kilns now. It is not meant to be run like a toaster! Good glazes are about much more than recipes, they are about firing schedules. None of the built-in "toaster schedules" have hold times on any segments, drop-and-hold sequences or controlled cools. Or even fire-to-cone accuracy. Yet such are a must for defect-free glazes, enhancing the effects of reactive glazes that must develop crystallization or variegation or firing accurately. It is easy to program: Tap the blue edit button to edit a program, tap a column of any segment to edit its value. Tap a segment number to delete or duplicate it. Google "bartlett genesis controller" for videos on creating and editing a schedule.

Context: When the cone does this I need to adjust the program, Manually programming a Bartlett V6-CF hobby kiln controller, Bloating on a range of bodies at cone 6: Why is this happening?, Be thankful for the hobby kiln controllers we have in North America, Bartlett Genesis Kiln Controller Programming, Firing Schedule, Kiln Controller

Thursday 16th September 2021

Fire organic ceramic shapes with this warping body for cone 6

Two warped small square planter shapes

Left is L4410K, right is L4410L. Very similar, but L has 5% more dolomite. And these cone 6 glazes work well, G2934Y left and G2936A right. These are slip-cast pieces, the walls are not super thin, but the straight-sided shape makes them more susceptible to warping and buckling. This effect can also be achieved using talc bodies, but they have the issue of being brittle, volatile, bloating and not fitting glazes. But both of these pieces have excellent fired strength at cone 6, they have a porcelain-like surface. Of course you will need to test shapes, adjust dolomite content and control firing temperature carefully to be able to do this with consistency. If you are near a Plainsman Clays distributor, they made a test run of L4410L (as the new L213), boxes are available for order. If not, you can mix your own.

Context: Warping

Sunday 12th September 2021

One reason why frits are such a good source of boron

A melt flow comparison between two glazes

These two glazes have very similar chemistries (except that G2931G has a much lower SiO2 content, that is why it is melting better). Left: 0.75 molar boron is being sourced by a high quality frit in G3879C, Fusion Frit F-524. Right: Ulexite is sourcing the same 0.75 boron. Ulexite is a natural material (it is mostly ulexite, but does have other contaminants). Unlike the frit, it contains volatiles that produce an LOI on firing, these gases are generated during the melting phase, producing obvious bubbling.

Saturday 11th September 2021

Three rutile blue glazes at cone 6

Three mugs with floating blue glazes

These are GA6-C Alberta Slip floating blue, AMACO Potter's Choice PC-20 Blue Rutile, GR6-M Ravenscrag floating blue. The clay is M390. The firing is cone 6, the schedule is C6DHSC (drop-and-hold, slow cool). The inside is GA6-B. The two on the left develop the blue color because of the slow-cool, the one on the right works on fast-cool because it contains cobalt (although it will fire somewhat more mottled). The centre one is a bottled commercial product, it was painted on in three coats. The result is quite compelling, this is a good place to start if you want the rutile-blue effect. Remember, these work best on dark-burning bodies.

Context: Ceramic Rutile, Ravenscrag cone 6 floating blue thinner and thicker applications, Ravenscrag Cone 6 Floating Blue on porcelain and a red stoneware, Rutile Glaze

Saturday 11th September 2021

An Alberta Slip based black passed all the leaching tests

Four black-glazed test tiles

This is the G3914A recipe on Plainsman M340 test tiles. They were fired at cone 04 using the PLC6DS schedule. We tested them in four different caustic liquids (using the GLLE test), there is no sign of leaching on any of them. This recipe contains only 4% black stain, that is enough to stain the base GA6-B glaze to a jet black. The surface has a unique iridescence not found in any other glossy black we have used.

Saturday 11th September 2021

What is the simplest, most practical raku base crackle recipe?

A glazed tile showing the raku crackle effect

Many people suffer high-percentage Gerstley Borate "bucket-of-jelly" raku recipes they find on line. Don't do this. There is a common Ferro frit that is perfect for this application, frit 3110 (Fusion frit F-75). All it takes is 15% kaolin (e.g. EPK) to produce and easy-to-use recipe that is guaranteed to craze. We have assigned it a code number of L4264, a raku base transparent recipe. We have also catalogued some common recipes that people use and outlined the issues they have: L4264A, L4264B, L4264C, L4264D. Do you need a white? It is a simple matter of adding 10% Zircopax to this.

Context: Raku

Saturday 11th September 2021

Are frits partially soluble? Yes, many are.

These 1 mm-sized crystals were found precipitated in a couple of gallons of glaze containing 85% Ferro Frit 3195 (we have seen these with frit 3249 also). They are cubical, hard and insoluble. Why and how to do they form? Many frits are slightly soluble, the degree to which they are is related to the length of time the glaze is in storage, the temperature, the electrolytes and solubles in the water, interactions with other material particles present and the diligence of the manufacturer in mixing, correctly achieving the target chemistry and firing. The solutes interact or saturate to form insoluble species that crystallize and precipitate out as you see here. These crystals can be a wide range of shapes and sizes and come from leaded and unleaded frits. In industry this issue is not generally a problem because glazes are used soon after being made.

Context: Ferro Frit 3195, A glaze slurry precipitates flakes, G2925B glaze can precipitate crystals like this over time, Precipitated crystals from a glaze having 60% lead bisilicate frit, Ooids in Glazes, Precipitation

Friday 10th September 2021

Contact Me

Use the contact form at the bottom on almost all the pages on this site.

Another Way to Support My Work

Subscribe to Insight-Live.com. It is about doing testing and development, not letting the information slip away. Starts at $15 for 6 months.


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 and learning from it will empower you. You will formulate and fix your own recipes and processes. Because it is on-line you can access your data from any connected device. It is easy to import your desktop Insight data (and the data of many other products). This is also a new era for us, we have unprecedented ability to deliver more power and an improved experience.

Teaching ceramics? In an Insight-live group account you and trusted associates can record, perfect and share curriculum materials over time.

Still using desktop Insight? Convert to the new system. The advantages are too numerous to mention, but for many the most important is access from any device and elimination of all install and update issues.

Group accounts for industry and education. Private accounts for potters. This is the future! Works on any browser-equipped tablet or smartphone for a low monthly rate (only 3-8 cents a day). Get started.

Conquer the Glaze Dragon With Digitalfire Reference info and software

Download for Mac, PC, Linux

Interactive glaze chemistry for the desktop. Free (but no longer in development).

Teaching ceramics? This is highly a focussed way to do it. Students can later upgrade to online Insight-live.com. Download here or in the Files panel within your Insight-live.com account.


What people have said about Digitalfire

  • Hi Tony, First, your website is the most knowledgeable and accurate information available on the internet today. THANK-YOU!
  • I have not been pottery long and I have decided to try to make my own glazes. Your web site is great. I like your cone 6 base glaze.
  • I want to comment. This is the most complete site about ceramics that I have ever seen.
  • Great customer service!!
  • You are so good for me. Find a stumbling stone and in a moment the path is easier.
  • Great Web Site, by the way, I have found a lot of your generously offered help and information very useful. Thank you!
  • 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.

What people have said about Insight-Live

  • Thank you again for the amazing website and wealth of information!!! InsightLive is proving to be an incredible asset as well!!!
  • First I want to thank you for the service you're providing the ceramics community at large.
  • If you didn’t know yet (most people don’t really express how they feel so I’m talking on behalf of the whole pottery community), you have become our most trusted & valuable ‘all things pottery’ resource. Thank you for your time, and the wisdom you share with all of us. I’m a humble newbie and i want to tell you how much I rely on the information you post and how much I appreciate everything you do. I want to name you ‘the clay angel!’.
  • I am learning so much from your website, even after 33 years in business as a ceramic producer.
  • 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 am a potter of over ten years and am now in this year paying attention to my glazes and what goes in to them. It's been an awesome journey with plenty of "ah ha" moments and exponentially more "what the..." moments. Regardless of what I'm feeling, digital fire is so far the best resource I've encountered. I’ve been going about glazes all wrong, following recipes and stabbing in the dark hoping to find one that Works for me... well, it’s not working! I’m devoting my time to explore glaze chemistry even more than I have and to do this I am convinced I can not go forward efficiently without a test kiln. THANK YOU for these wonderful resources!
  • Many thanks for your time and trouble, re the information cone 6. You are a wealth of generosity and help to the home Potter.



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

1