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Transparent over-glaze for cone 6 stoneware
Is a good one even possible on brush decorated ware?
The mug on the right is terra cotta slipware fired at cone 04 using underglazes and a leaded transparent over-glaze (lead glazes are still commonly used in many parts of the world and considered safe there). Mug on the left: This potter wants to use the same technique on cone 6 stoneware. This is a typical transparent glaze (fluxed using a frit or Gerstley Borate). The result is micro-bubble clouding, boron blue, washed-out colors and surface defects. Because it is a dipping glaze it went on too thick and didn't cover well over the colored brushstrokes. However, achieving better warm browns is possible. A more refractory underglaze (made with stains, not iron oxide) that does not bleed. A more fluid melt transparent glaze that is better able to shed bubbles. A drop-and-hold firing would reduce surface defects. Finally, careful control of the glaze thickness and quality of laydown. To achieve the latter, it might be worth preparing the transparent as a brushing glaze, at least for application on the outsides (enabling a dense and even laydown over the whole surface).
Context: Why dipping transparent glazes.., Underglazes require a fluid.., The right transparent glaze.., Engobe, Underglaze
Tuesday 23rd September 2025
Stains are better in black glazes
5% stain vs 15% metal oxides
Consider the hazards and hassles before choosing a black matte or gloss recipe that has high individual or combined percentages of manganese dioxide, cobalt or nickel.
Gloss blacks: These are super popular right now as the base for layering of reactive glazes. DIY dipping versions thus make a lot of sense. They make even more sense when they don’t turn to jelly in the bucket because of the high percentage of red iron oxide in all blacks made using metal oxide colorants. And when the total percentage of pigment is as high, or higher than 15%. And when the pigments cause crystallization (especially when overloaded).
Matte blacks: The human eye can detect even slight differences in the degree of matteness (which is very difficult to keep consistent). Raw metal oxides affect the matteness, especially when overloaded with pigment. They are prone to cutlery marking if too matte. By using stains manufacturers, and even potters, have learned to tune recipes (lower left) and firing schedules to achieve consistency and functionality (even tourist souvenirs (lower right) feature them now). With stains, only one material is producing the color, its percentage (which can be as low as 4%) can be tuned.
Context: Ceramic Stain Toxicity Label.., Control matteness by glaze.., Heres evidence that using.., Ceramic Stain, Toxicity
Thursday 18th September 2025
Thickly applied slips must fit the body and each other
Fit? It has to stick well. And stay stuck during drying (and shrinking). And the bond has to survive shrinkage that happens during firing. This potter is doing thick applications of each slip (actually that makes them engobes). She uses stains, that's wise, metal oxides bring baggage when used to color slips (e.g. their decomposition can affect the bond, they can gel the slurry, flux the fired product thereby increasing the firing shrinkage of the slip). Stains are better because they affect slurry and fired properties less. But there are still enough issues that each colored slip deserves testing. This potter first slaked B-mix as a slip (it is highly plastic), using it at a runny yogurt consistency. But it bubbled when fired hotter than a cool cone 6. A switch to porcelain slip (which is non-plastic) is shown here. It flaked off as it dried (even in a damp box for 24 hours), also after bisquing to cone 08, and sometimes even after firing to cone 6. This signalled a drying mismatch between body and slip, the bond that managed to survive drying was weakened enough to fail on firing.
The solution was an engobe recipe that is super plastic and sticky. The popular Fish Sauce recipe is an example, it contains 10% bentonite and is unbelievably sticky. We formulated L3954B with this in mind. It adheres well to leather-hard clay and doesn't flake off (misfit is instead evident by surface cracking if its shrinks more than the body). And it is not highly vitreous, keeping its fired shrinkage low enough to match stoneware bodies. Mixing your own recipe also enables compensating the amount of feldspar if the stain affects the slip's degree of vitrification, and therefore fired shrinkage (e.g. blues, oranges, yellows).
Context: L3954B, This pottery glaze is..
Monday 15th September 2025
A giant cookie-cutter for slab built mugs
View and print it now using the Downloads page link
Available on the Downloads page
3D print four of these and glue them together to make a large cookie cutter for producing slab-built mugs. 3D print the cup, fill it with plaster and remove the PLA using a heat gun. Roll out a thin slab of clay, press the cutter into it using a round wooden batt, make sure it is not sticking to the board and flip it over onto the plaster form. Handles can even be attached while it is on the form. If clay is plastic it can be used quite stiff. Experiment, adjust sizing and dimensions and reprint to fine-tune.
This has been drawn "parametrically" with OnShape. I only had to draw half of one of the quarters (I mirrored that, extruded and then did a circular pattern of 4). The downloads page (link above) has a free link to view this drawing at OnShape.com. To 3D print, right-click the part (from the list on the lower left, "Quarter 1" and "Cup"). Choose the Export option and select 3MF as the file type (it should go to your downloads folder). Open it with your slicer and print (turn the quarter over and make four). You can even export in formats that other CAD software can open. Better yet, import it into your OnShape account to see the design history and change multiple aspects of the geometry in the variables panel (the drawing will adjust automatically). Other dimensions (e.g. cut depth) can be edited manually. Parametric design is revolutionary and it is now accessible even to hobbyists; it fits my try-it, adjust-it and try-it-again way of working.
Context: Large cookie-cutter 3D-printed in.., 3D Design, Pie-Crust Mug-Making Method, Cookie Cutting clay with..
Monday 15th September 2025
Recognize these universal oxidation glazes?
Almost every potter needs a Albany brown and rutile blue.
These are made by Barbara Childs Pottery (I saw them on sale in a tourist shop in Alaska). To keep costs down, I first assumed they use dipping glazes they mix themselves. Potter's Choice PC-32 Albany Slip Brown and PC-20 Rutile Blue hobby glazes emulate these long time pottery glaze recipes. However, a reader noted that Barabara Childs uses Clay Art Center’s Stellar Rust and Floating Blue (with guest appearances by Blue Green). But Amaco and Clay Art don't just use the traditional recipes; they adapt and improve them. Consider the rutile blue. Neither is using the traditional G2826R floating blue recipe, there are new and better ways using recipes like GA6-C and GR6-M. Likewise, with the brown, they are not using the traditional G2415E Albany Brown recipe. Rather, they improve it (e.g. like we did with G3933G1). High on their list of improvements would have been a way to reduce or remove the lithium to cut costs. Maybe you are a hobbyist and don’t feel you need to DIY your costs down. But do your customers feel the same way? Not buying just ten small jars of hobby brushing glaze will pay for a mixer and much of the ingredients to make gallons of each of these as dipping glazes. It will also set you on the road to gradually improving the glazes you use. And even reducing your prices. What about buying premixed powders? Yes, that is much less expensive. But if you are mixing the glaze from one manufacturer with the clay body from another, crazing is an ever-present issue. Mixing your own enables an adjustment to fix the problem.
Context: Adding 6 lithium carbonate.., PC-2 floating blue with..
Tuesday 9th September 2025
A draining issue with a slip cast bottle
It is turning inside out!
Why did this happen? There is a perfect storm of factors. Draining, during slip casting, creates suction and slip is heavy (1.8 times heavier than water). And this mold is tall with a narrow neck. So that creates a lot of suction. A slip having inadequate fluidity complicates draining. This round shape, even with printing artifacts, also releases well. How can this issue be avoided?
-Draining the mold carefully, holding it near horizontal for much of the drain.
-Use a well-deflocculated slip.
-Add bentonite to the slip, perhaps 0.5%, to make it stickier and slow down release time (which also slows down the casting time).
-At times, this will happen despite all efforts. In that case, if might be necessary to use a tube (e.g. 1/2 or 5/16”) to pump most of the liquid slip out of the bottle before inverting it. Adapt a 3D printed pour spout to keep the tube centered, at least near the mouth of the bottle.
Context: Slip Casting, Beer Bottle Master Mold.., Casting Slip Problems
Saturday 6th September 2025
OnShape CAD is Free for Hobby Makers:
Is it as good as Fusion 360?
It is very hard to let Fusion 360 CAD go. But the approaching $750 renewal is powerful motivation! OnShape is amazing. There is nothing to install, it runs in a browser tab like Google docs (see picture below). Sure, it won’t run offline, but I am almost never offline. It functions very similar to Fusion 360 for my basic requirements of making molds for slip casting. Recent experience with the complexity and slowness of Solidworks for Makers, which is total overkill for what I need, really makes OnShape look good.
My OnShape drawings are stored in my cloud account and are public. That sounded bad at first, but it also means that they are shareable with others (another person, whom I choose, can actually work on a drawing at the same time as me). The full OnShape is working in Firefox on my 2014 Mac Mini Ubuntu Linux machine. This is beyond exciting to me, traditional CAD has always required expensive hardware that is far beyond a hobbyist (of course, OnShape will also work in Safari on Mac and Chrome on Windows). A real bonus: I can edit drawings on iPad in what appears to be full power mode (although a mouse and keyboard are needed for serious work).
Besides the above, here are some of the features and advantages I am seeing:
-It opens and exports many professional CAD file types (a major drawback in SolidWorks for Makers).
-It is really fast, login is quick and a drawing can be open in seconds, this is way better than xDesign for Makers (from Solidworks).
-Documents are always saved, close one by simply clicking the home icon on the upper left.
-The timeline (called the "Feature Tree") can be reordered, turned back and has folders like Fusion 360.
-To 3D print just select part of your drawing, right-click and choose to export it in 3MF or STL format (it goes into the downloads folder).
-All tools are in one long, monochrome ribbon of tiny icons at the top but there is a tool searcher.
-Like Fusion 360, sketching constraints are inferred as sketches are created and applying them works in a similar fashion (but more aggressively). Their tiny symbols display in groups and associate to the point or line by a light grey line. Automatically applied constraints can make sketches behave in strange ways until you learn to find and remove the offending ones.
-Constraints and dimensions are movable so drawings can be uncluttered for printing.
-Section analysis is in the "Camera and Render Options" pop-up under the view cube.
-The spline and bezier sketching tools are not as interactive (a downside of running in a browser).
-It is not as good for making cookie cutters because it doesn’t do text nearly as well).
-Parameters, called variables, are more in your face; they are even shown in the timeline.
-Panning, rotating and the viewcube work a little differently. The iPad version of OnShape beats Fusion easily in this respect.
-OnShape does not appear to support text along a path like Fusion.
The secret weapon of learning OnShape: An AI chatbot. Just ask any question about how to do something. One helpful migration from Fusion 360 is to print the sketch(es) (with constraints and dimensions) and work from that to create the equivalent in OnShape. An advantage of OnShape is that if you get stuck (e.g. drawing goes red), you can share a link with a more knowledgeable friend to tell you what is wrong. Most often the issue is conflicting constrains.
Context: 3D mechanical design software.., 3D Printed Pour-spout Forms.., My Breakup with Fusion.., OnShape parametric cloud-native CAD..
Saturday 6th September 2025
Classic Medalta Potteries Beer Bottle
Make this mold using OnShape and Fusion 360
Danny Downsized: He's Being Outsourced.
He should have seen this coming!
Management now thinks they can outsource his technical work. Danny was good, but he didn’t build a centralized, searchable record of material testing, shipment histories, specs, production problems, and solutions. Instead, his knowledge is buried in thousands of Excel and Word docs and PDFs. He should have used Insight-Live.com to organize, interlink, and preserve this critical data. Sadly, the company does not even realize what they face without Danny:
- Slower problem-solving and loss of institutional memory.
- Greater dependency on outsiders who lack long-term investment.
- Inability to verify product claims.
- Quality drift leading to recalls, rework, and higher warranty costs.
- Innovation slowdown.
- Eroding customer trust and ballooning consultant costs.
Had Danny been not just a watchdog but a technical innovator, suppliers and consultants would have been secured to support—not replace—his in-house expertise.
Context: Protect your reputation as.., 2 Skids of Material.., Tommy Turnback Ignored AI..
Sunday 31st August 2025
Tommy Turnback Ignored AI
By not adapting he wrote his own layoff notice
Management says AI can do most of the technical work now. Tommy had no automation, no models, no data pipelines. Just “the way we’ve always done it,” trapped in spreadsheets and sticky notes. When the new AI system went live, his expertise didn’t plug in. It got left behind!
- The AI could really have used his seasoned human oversight.
- Years of hard-won knowledge lost in a digital junk drawer.
- Outside consultants are charging a premium to relearn what he already knew.
- Errors slip through because no one taught the machines better.
- Innovation stalls while the company rebuilds what he could have bridged.
Technicians aren’t just there to keep things running—they should teach the future how to work. Refusing to adapt doesn’t protect your job. It writes your own pink slip.
Context: Danny Downsized He's Being..
Sunday 31st August 2025
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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 want to also thank you for all you have done for the ceramic and pottery industry.
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What people have said about Insight-Live- I am eternally indebted to you for all that you have done to advance the technical abilities of non-industrial pottery! I love using Insight.
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- Love the email I got today about the clear glaze because I have an account! Thank you for all you do. These emails are a great idea.
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