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

Are these optical pyrometers suitable for a potter?

Notice the title says "Emissivity Adjustable". That is important because for accurate measurement, the emissivity of the object you point the gun at, near the temperature needing accurate measurement, has to be known accurately. In industry consistent results with this type of instrument depend on always aiming the gun, at right angles, at a specific target in the kiln (e.g. a firebrick), whose emissivity is known exactly (from the technical data from the manufacturer) and which has a surface of consistent roughness that remains stable firing-after-firing. If you are a potter you do not have calibration instruments and emissivity data. And you are probably not inclined to carefully set a piece of kiln shelf, for every firing, vertical at right angles to the peephole and blocking view of the cones! Even if you do, remember the gun calibrates to one temperature. And getting it to work is a matter of waving this plastic fun in front of and open peephole and hoping for the best before it melts! Perhaps it is better to spend this money on thermocouples instead.

Context: Thermocouple

Friday 21st January 2022

The same oatmeal glaze on the same body at cone 5 and 6 oxidation

This is the G3933 recipe on the outsides of these mugs (the inside glazes are L3500G.). The body is L4471D, it is being targeted at cone 5. At cone 6 (right) the speckle in the outside glaze, from the iron addition, is slightly more vivid (the drop-and-hold and slow-cool on the firing schedules also helps develop the speckle). These were fired using the C5DHSC and C6DHSC schedules. The color bleeds less across the boundary on the lip at cone 5.

Thursday 20th January 2022

Fixing a crawling problem with a measured CMC addition

A pail of glaze needs CMC gum

The problem: This dipping glaze is crawling (as shown on the glazed tile). Fortunately, the slurry has settled about an inch, that provides an opportunity for an immediate fix: Remove some of the water and replace it with gum solution. I want to replace about one tenth of the water (to be between a base coat dipping and brushing glaze). The bucket calculates to 2549g of powder so I need to remove 217g of water and replace it with gum solution. One way is to use a small sponge: Wet and wring it out and then repeat touching it to the water surface and wringing it out into a container until 217g. A propeller mixer is needed to mix in the added gum solution (it won't just stir in). Of course this degree of weight-precision may seen to be overkill, but having a record of what was actually done to adjust the slurry is important to repeating it the next time it is prepared or as a base for further adjustments.

Context: CMC Gum, CMC Gum Calculator - Worksheet

Thursday 20th January 2022

Amaco underglazes can contain very high percentages of stain

Top are V-326 and V-388 underglazes, painted on and 04 bisque fired. Although the layer is very thin the coverage is amazing and the brightness is stunning. This degree of brilliance is not possible unless the percentage of stain is very high. That explains whey these are double or triple the cost of a typical commercial glaze. The bottom mugs are clear-glazed and 05 fired, the one on the left with Amaco LG-10 and the one of the right is Spectrum 700. The latter produces better results over the underglaze and is more transparent and less yellowish on the body.

Context: Underglaze

Tuesday 18th January 2022

How to convert a dipping glaze to a brushing glaze

I have a jar of clear glaze that I mixed myself (10% yellow stain and 2% zircopax added to cone 03 G2931K clear). Commercial glaze producers make their lines of glazes like this. The cost of the dry materials: About $6. How can I make it paintable? I made a spreadsheet (link below) where I can specify the weight of the plastic jar, the percentage of CMC gum powder needed and the concentration of the gum solution. I just need to weigh the jar of glaze (without lid), weigh a teaspoon of the liquid glaze (lower left), dry it (upper right) and weigh the dry (lower right). After filling in these numbers the sheet tells me what weight to evaporate the jar to and how much gum solution to mix in. It paints on just like a commercial glaze. Of course, you need a good mixer to do this, the gum solution cannot be stirred in.

Context: CMC Gum, Where do I start in understanding glazes?, Fixing a crawling problem with a measured CMC addition, A case where glaze thickness really matters, CMC Gum Calculator - Worksheet, Brushing Glaze, Dipping Glaze

Tuesday 11th January 2022

Making a QRCode using porcelain pixels

A QRCode made from porcelain pixels

I 3D-printed a stamper to create 9mm square pixels. Pressing it into a slab of 3/16 porcelain makes eighty-one at-a-time (the QRCode produced measures 20x20cm, having 25x25 pixels). The black porcelain has 5% Mason 6666 stain. Firing temperature was cone 6. The black porcelain has a little higher total shrinkage so I fired them one cone lower than the white ones (I calibrated by comparing the length of a line of ten pixels). The pixels dry and shrink and drop out of the stamper easily. The action of the stamper rounds the upper corners of each. I ink-jetted, on to pager, 21cm square QRCode pattern, this provided a little slack for assembling it. Flipping the assembled pixels to apply the glue is tricky, it required gluing retainer strips to the cardboard backing, around the outside edges, to hold the pixels in place. For the next one I plan to glue the pixels to a zero-fired-shrinkage clay tile, made from L4410P. A little silicon sealant on the tile and that will be suitable outdoors. What does this QRCode say? https://plainsmanclays.com.

Context: Porcelain pixel QRCode is scannable. Try it!

Monday 10th January 2022

Why you need to make your own glazes, fire your own kilns

Are you a potter that depends on glazes made by others? Do you have your ware fired in someone else's kiln? Cannot mix clay body tests? Then the evolution of the quality and aesthetics of your work is being stunted. This mug is a good example of why. This is G3933, version 1 of an oatmeal we made by adding iron, rutile and tin to a 75:25 blend of our base matte and glossy glazes. It is crawling at a few sharp angles of the incised decoration, that means it needs a little CMC gum. And, it is not quite matte enough, we need to switch to an 80:20 blend. Third, the red-burning body gives better color at cone 5, and this glaze melts well in a C5DHSC slow cool firing. So I will include it with other cone 5 bodies and glazes we are testing (because I want to move down from cone 6 to save energy and elements). Finally, I would like the glaze a little darker so I will test increases in the rutile and iron. All of these changes are on my radar because I make my own glazes and have my own test kiln.

Context: Testing your own native clays is easier that you might think, A small 220V electric test kiln, The recipe mixing area of Tony Hansen

Sunday 9th January 2022

You may know Veegum T but do you know VeeGum CER?

Attempts to use a glaze that is too thick

The glaze in this jar was 'goop', impossible to paint on because it was too viscous. And it dried way too fast. Laguna mentions adding water so I measured the specific gravity (SG): 1.7. That is super-high, it took a 125cc addition to bring it down to 1.5, but it was still thick, dried even faster and brushing it on evenly was even harder. It was not obvious what to do next. It needed a lot more water (1.3-1.35 SG is normal to support multi-layer application), adding CMC gum and enough water to do that would produce an unusable watery and sticky slurry. Veegum CER to the rescue! It is a 50:50 mix of CMC gum and Veegum T. The former slows drying and hardens, the latter gels. So it can simply be added until the painting properties are right. And, a Veegum CER solution is easier to handle than one of CMC gum. This really worked! The brushing properties are just right and it gels nicely on standing. CER is also good for highly fritted dipping glazes or others lacking in clay content (otherwise CMC might still be better).

Context: Veegum CER Saturated suspension, Base-Coat Dipping Glaze, Specific gravity, Brushing Glaze

Wednesday 5th January 2022

Common dipping glazes converted to jars of brushing glazes

These are cone 6 Alberta Slip recipes that have been brushed onto the outsides of these mugs (three coats). Recipes are GA6C Rutile Blue on the outside of the left mug, GA6F Alberta Slip Oatmeal on the outside of the center mug and GA6F Oatmeal over G2926B black on the outside of the right mug). One-pint jars were made using 500g of glaze powder, 75g of Laguna CMC gum solution (equivalent to 1 gram gum per 100 glaze powder) and 280g of water. Using a good mixer you can produce a silky smooth slurry of 1.6 specific gravity. However most commercial glazes do have a lower specific gravity (have more water), this does aid further in paintability but requires more coats. Amazingly, the presence of the gum also makes it unnecessary to calcine the Alberta Slip.

Context: CMC Gum, Where do I start in understanding glazes?, Brush-on commercial pottery glazes are perfect? Not quite!, Brushing Glaze, Glaze Layering

Wednesday 5th January 2022

Veegum CER Saturated suspension

This is the most viscous suspension we can make, 300ml water with 13.25g Veegum CER (50:50 mix of Veegum T and CMC Gum). It required the use of hot water and our two-gallon-mixer, on its highest speed, mixing in this cup. Add this gel to a raw glaze to improve its brushing properties and slow down drying. Often this works better than CMC gum alone because it gels the slurry enabling increasing the water content and improving suspension properties. Or, substitute this for part of the water in low-clay-content recipes (if the glaze is already viscous, just add this). In slurries having sufficient clay use pure CMC gum instead (unless a high-water-content slurry is needed).

Context: Veegum, CMC Gum, You may know Veegum T but do you know VeeGum CER?

Wednesday 5th January 2022

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. 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

  • I have read just about all your articles on Digitalfire and use your software, really appreciate the wealth of knowledge and testing you bring to ceramics.
  • Firstly, I want to thank you about this very good site in the net which helps very much in the development of the ceramics industry.
  • Thank you for the work you do to improve the work of potters trying to do new things.
  • Tony's site is really full of exceptional technical information.
  • I have been perusing through some of the level 2 areas of your site and am just in awe of what a great resource you have developed.
  • I'm all right brained..... I have the serial number. My computer is finally going. Thanks for the service. I love my Digital fire.
  • DID I TELL YOU I LOVE YOU ... you made me feel so much better!!! I was stressing that I will never figure out how to resolve issues b/c it always seems like an new hurdle to get over ... thanks for that email again I feel empowered again.

What people have said about Insight-Live

  • I have done production pottery at cone 10 and 5 for 40 years, but during almost of full year of downtime due to COVID, I am exploring low fire terra cotta. Digital fire is an amazing resource. Thank you so much.
  • 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.
  • Thank you for your time, and I am totally excited that I woke up to an email from Tony Hansen (I’m a big fan)
  • This site is an incredible resource and I just want to thank you for it. It fills in so many gaps from my studio art ceramics education and has made me more confident in the pieces I sell. I reference it almost weekly and have recommended it to so many other potters. The ceramics world is better off learning and applying this wisdom and I'm so happy to see someone teach so technically and seriously about the material. Culturally, there is a casualness in the pottery world (whether in community studios or school art rooms) that is borderline negligent in some ceramic circles and I just really appreciate when I see someone pursuing excellence and technical mastery of the material. Because it really matters!
  • I'm glad I was of some small service. Your whole venture is a marvel. All the best as we go forward.
  • 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.
  • Thanks! I look forward to seeing your posts. I have read and printed many things you have posted over many years. Have learned a lot from you.



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

1