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COVID-19 Alert

Effective March 7, 2022 entry to our facility will open for customers, however, the following guidelines will remain in affect.

  • Only two customers permitted in office at a time.
  • Face masks remain mandatory and will be supplied if you do not have one.

We will continue to monitor and review the Covid-19 situation in our area and update our entry guidelines as deemed necessary.

Curbside pick up remains an option for those who do not wish to enter our facility.
Orders can be placed via phone at 403-527-8535, fax 403-527-7508 or click on email for listing of contacts for additional assistance email. For more Covid-19 info click here.

We appreciate your business and thank you for understanding the measures we continue to implement.

Technical Tips Blog

Ravencrag Slip vs Alberta Slip floating blues at cone 6 oxidation

Two floating blue mugs

Usable, reliable, non-crazing floating blue glazes are difficult to achieve at cone 6. Not these, they pass all the tests yet fire like the original classic G2826R floating blue from David Shaner. Both have been applied at moderate thickness on Plainsman M325 (using a slurry of about 1.43-1.45 specific gravity, higher values end up getting them on too thick). The Ravenscrag version highlights contours better (the edges are black because of the black engobe underneath). It also produces the blue color whether or not the kiln is slow-cooled (although drop-and-hold PLC6DS schedule usually fires more blue). The Alberta Slip version has zero cobalt so it is less expensive to make (but it does require the C6DHSC slow-cool firing schedule). It produces a deeper color over the L3954F black engobe on these pieces. Both of these produce a wide range of effects with different thicknesses, bodies and firing schedules.

Context: GA6-C, GR6-M

Wednesday 28th September 2022

Ravenscrag floating blue color affected by cooling speed

Two floating blue mugs

Ravenscrag Slip really shines in its ability to produce a good floating blue glaze at cone 6, this is the GR6-M recipe. The speed of cooling in the kiln affects the appearance. The mug on the left was cooled faster, using our drop-and-soak PLC6DS firing schedule. The other one was slow-cooled using the C6DHSC schedule. The latter schedule is preferable for these because the G3914A black has a much smoother surface. The blue could be recovered by adding more cobalt.

Context: GR6-M

Wednesday 28th September 2022

A gummed engobe made this possible

Mugs with black engobed bases

This is L3954F cone 6 black engobe (these mugs will also be glazed completely black). Three factors make this workable. First, a non-gummed dipping engobe will not work for this (it will not apply by brush evenly or thickly enough). To make the brushing version we mixed 500 grams of L3954F (with black stain) into 280g water and 75g of Laguna Gum Solution. Second, the recipe is tuned to have the same degree of vitrification as the body so pieces won’t stick to the kiln shelf during firing. Third, this procedure introduces a possible issue: Applying the engobe rewetted the bases of these leather hard mugs, extending drying time. Since the handles were in danger of shrinking too much as the bases caught up I painted gum solution on the thinner sections to slow down their drying.

Saturday 24th September 2022

Mother Nature's Porcelain: The lumps in the quarry

Mother nature's porcleain lumps

This 50 lb lump is from a quarry where we are mining the Whitemud Formation in southern Saskatchewan. This layer is extracted from the top of a hill at the bottom of a valley, putting it more than 50 meters below the prairie surface. The lumps are extremely dense and very heavy. They are also quite damp, about 12% by weight fossil water. They exhibit this horizontal layering, a clear indication of the sedimentary nature of the deposit. The clay is exceedingly fine-particled and the silica present exists in rounded grains finer than about 150 mesh. There are flecks of high-carbon material and some tiny iron particles. When lumps like this dry out when exposed to the sun they break down into thousands of pure-white pieces. These dry lumps slake quickly in water to create a creamy smooth slurry from which I can easily sieve out the carbon and iron particles to produce the hyper-smooth natural porcelain.

Context: How to Find and Test Your Own Native Clays, Mother Nature's Porcelain - Plainsman 3B

Friday 23rd September 2022

Pure nepheline syenite mug glazed and fired to cone 02

A nepheline syenite mug

It is near stoneware strength. How was it possible to make this? Actually, it is 90% nepheline syenite and 10% bentonite. The latter imparts enough plasticity that it can be thrown easily on a potter's wheel. By about cone 1 it begins to warp. This is fired to cone 02 with standard Spectrum low fire glazes. No crazing is evident and the coverage is normal. The next stage will be to use Veegum to get a 95:5 mix, then we will bisque to cone 01 for translucency and then glaze fire at cone 04. This really demonstrates the amazing ceramic properties of this material. We aged this for several weeks before throwing and it was stable and unchanged in softness or plasticity.

Context: Nepheline Syenite, Custer Feldspar vs Nepheline Syenite at cone 8 oxidation, Pure Covia nepheline syenite fired at cone 2, 1 and 04

Friday 23rd September 2022

Testing a found clay for its pottery suitability: First steps

Would you like to be able to use your own found-clays, ones native to your area or even your property, in your production? Follow me as we evaluate a mystery clay sample provided by a potter who wants to do exactly this. I will use ordinary tools that any potter either already has or can buy at low cost. We will describe this clay in terms of plastic clay bodies and common ceramic materials that most potters already use. The potter who submitted it has worked enough with the material to suspect it has potential and he wants to know how to best utilize it (e.g. at what temperature, with what glazes, mixed with what, processed in what way). In technical terms what we are doing is called "characterization".

Context: Evaluating a native clay's suitability for pottery

Sunday 4th September 2022

Here’s how to remove agglomerates in a gummed engobe

This brushing engobe is thick and gooey (because it contains CMC gum), so it is very difficult to sieve. It contains tiny lumps of New Zealand kaolin that our propeller mixer is not able to break up. But 30 seconds in this kitchen blender and a litre of it is as smooth as silk.

Context: This is how New Zealand kaolin powder agglomerates, Engobe, Agglomeration

Sunday 4th September 2022

Iron red on porcelain and a red burning stoneware

Iron red glazed mugs

This is the G3948A recipe fired to cone 6 using our standard C6DHSC schedule. The color "breaks" to black where thinner around contours so it seemed like a natural that the inside glaze should be G3914A Alberta Slip black. The contour of the foot ring is important or the glaze will run onto the kiln shelf. My standard fluted ring foot is working well. An option would be to glaze the bottom inch or so with the black and the iron red down to that.

Context: Stop a runny glaze with another glaze!, New iron-red glaze on porcelain at cone 6 oxidation

Tuesday 16th August 2022

New iron-red glaze on porcelain at cone 6 oxidation

Two iron red mugs

This is the G3948A recipe. Iron red glazes are easy to do in high-temperature reduction but not so in medium-temperature oxidation. Most people just try a bunch of recipes they find online hoping that one of them actually fires the way it is shown in the picture! A better approach for us was to study a range of ones claiming to be iron reds looking for things in common with the chemistries and recipes. G3948A, on these two M370 mugs, is a product of that. Unlike many, the original recipe we found, G3948, did have a suggested firing schedule. It seemed strange so we just used the standard C6DHSC slow-cool schedule. That one is also ideal for the liner glazes, giving them a better gloss finish. It was not tempting to even try the original recipe (because it measured up poorly against common sense recipe limits), but it did make sense to fix obvious issues and then try it. Unlike every other recipe we have seen, this one suffers no issues with gelling of the slurry because it contains no Gerstley Borate and uses black iron oxide. It has very good application properties and requires only 80 water for each 100 powder to mix as a creamy dipping glaze. And it does not need any lithium carbonate.

Context: Iron red on porcelain and a red burning stoneware, Iron Red Glaze

Sunday 14th August 2022

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.

Context: Silicone sealer for porous ceramic for outdoor use, ModPodge clay sealer

Friday 12th August 2022

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Plainsman Clays Ltd., 702 Wood Street, Medicine Hat, Alberta T1A 1E9
Phone: 403-527-8535    FAX: 403-527-7508