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Technical Tips Blog
Mod Podge clay sealer
Available at Walmart, Amazon, Michaels and others. It was water-based, non-toxic, "top-rack dishwasher safe" and dries to a hard finish. This makes it potentially useful to seal porous ceramic such as terra cotta and dolomite or talc white-burning bodies, even functional ware.
Friday 12th August 2022
Large Snow plate fired at cone 04
The plate was made by Karel Peeters, Aug 2022. The glazes are from Spectrum, they are watered down and applied using a gravity feed sprayer. It is the higher porosity of Plainsman Snow that makes the use of these watery gummed glazes possible (older talc bodies would not have worked with this method). Large pieces like this are extremely difficult at stoneware temperatures because of difficult drying, high firing shrinkages and extended firing schedules. But these are non-issues with Snow, it is super plastic yet dries exceptionally well, has zero firing shrinkage and can be fired in a fraction of the time! These factors coupled with the brilliant colors possible at low temperatures make this body an attractive option for potters to make extra money with less effort.
Friday 12th August 2022
Terra Sigilatta surface on a dolomite white earthenware
The clay is Plainsman Snow fired at cone 04. August 2022 by Nina Berinstein. Very thin and light pieces can be made without danger of warping during firing (because this clay as zero fired shrinkage). This piece was treated with Mod Podge, this has sealed it against water penetration and not affected the appearance or texture.
Friday 12th August 2022
The Iron Red mechanism is working in one base but not the other
These two pieces were fired in the same kiln using the C6DHSC firing schedule. Fluid melts are an essential enabler of crystal growth during cooldown, both of these contain significant Li2O to help the B2O3 achieve that. Glaze #1, G3948A, has less iron than is typical and much more MgO/CaO. Glaze #2 has much more Na2O and it has both SrO and ZnO that #1 does not have. #2 is much higher in Al2O3 and has more than double the amount of SiO2. So which of all these factors is responsible for #2 having zero crystals? Very likely its low CaO/MgO levels. Fixing it does not appear practical because of the "major surgery" needed to exchange ZnO/SrO for MgO and the extra B2O3 needed to restore the melt. Since #1 has a low thermal expansion it should fit most bodies anyway.
Wednesday 3rd August 2022
Delflocculation is a "magic process", appreciate it
Casting slips require a minimum of water. Amazingly, it is possible to get this 3000g of M370 powder into only 1100g of water! And the fluid slurry produced, 2250cc, still fits in the container. How is this possible? That water has 11 grams of Darvan 7 deflocculant in it, it causes the clay particles to electrolytically repel each other! An awareness of “the magic” can help give you the determination to master deflocculation, the key enabler of the slip casting process. Determination? Yes, the process is fragile, must develop the ability to “discover” the right amount of Darvan for your clay mix and water supply. And the ability to recognize what is wrong with a slurry that is not working (too much or little water, too much or little deflocculant).
Saturday 30th July 2022
Drying shrinkage + firing shrinkage ≠ total shrinkage
Plainsman Clays, for example, publishes dry and fired shrinkage data for their clay bodies. The former is the shrinkage from wet-to-dry. The latter is the shrinkage from dry-to-fired. You cannot add the dry and fired numbers together to get the total because the two are based on different starting points. Consider this example: 6.25 dry shrinkage + 6.66 fired = 12.9 whereas the actual total shrinkage is 12.5%. Shown is the way to calculate the total shrinkage correctly if you only have drying and fired values (thanks to Tom Hittie for deriving this for us). Of course no one is going to bother actually doing this calculation! So just remember that the actual total is a little less than adding the two together.
Monday 25th July 2022
Liquify a pint of brushing glaze so well it does not need sieving
This photo shows a method we used to use for adding CMC gum solution to glazes to make them brushable, this made it possible to produce high specific gravity slurries. But we don't do it this way any more. The reason is that kitchen blender. It can mix a slurry containing gum powders quickly and thoroughly, even on low speed. There is another thing we also do now: Make low specific gravity glazes, they are more brushable. That can be accomplished by also adding Veegum (it also gels the slurry). Commercial brushing glazes are made this way, that is why they often require many coats to get adequate thickness. In this example of cone 6 black G3914A, we added 5g Veegum and 5g of CMC gum to 340g of ball milled glaze powder. After shaking it together in a plastic bag and adding it to 440g of water the blender turns it into a gelled slurry that is a delight to paint with. This process produced just the right amount to fill a 500ml jar.
Friday 22nd July 2022
Alberta Slip based black passed all four leaching tests
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.
Context: Liquify a pint of brushing glaze so well it does not need sieving, Cone 6 oil-spot glaze effect, what works and does not work?, Two black cone 6 glazes recipes. One is much safer., Your supplier is out of stock on glossy black glaze? We made our own.
Sunday 17th July 2022
A practical dust collector you can make
An example of a custom-made dust collection hood in our repackaging and lab recipe mixing area. The slots along the front suck particles into the duct directly away from the operator's face. Suction comes from a centrifugal exhaust fan downstream where the pipe exits the building, it is driven by a 3/4hp motor (these fans are best at sucking, not blowing, so they need to be located at the exit). About 40 feet of 8 inch heating pipe connects from the hood to a fitting that expands to 12 inches going into the fan. The sliding damper above the hood enables stopping all airflow (to prevent heat loss during cold days). Notice it is located above the scale and heat sealer where most dust is generated during weighing and packaging.
Friday 15th July 2022
Gold decal on a gunmetal matte black glaze
This is a cone 6 porcelain mug and glaze. We get this satin matte effect in our test kilns using the PLC6DS schedule. Larger kilns cool slower so this glaze will turn out more matte, possibly too matte. When needed we deal with that by increasing the percentage of glossy base (this is a 15:85 blend of G2926B glossy and G2934 matte with 6% black stain). The decal is from Sanbao Studio. On the left, it has just been applied. But, other than the glossy finish revealing its location, no gold design is visible. But, after the decal firing, using the MDDCL schedule, we get the result on the right.
Context: Ceramic Decals
Saturday 9th July 2022
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