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Plainsman Pottery Supply is open for in-store shopping.

Pickup orders may still be placed via email at larry@plainsmanclays.com, or over the phone by calling 780-440-4791.

Click the links to the left to get information and pricing on our products. Click the "Plainsman Data Sheets" for details information on the use and Plainsman clay bodies and glazes. The blog below is intended to help you with all manner of technical issues in ceramic hobby production, these posts come every few days, so check back often.


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Technical Tips Blog

First mug in my newly created mold

Slip cast mug

This test mold is thin-walled yet I can cast three thick-walled mugs in three hours. This clay is L2596G, a buff burning cone 10 stoneware - the mug on the lower right has been fired to cone 10 oxidation. Achieving 4-5mm thick walls is not a problem if the casting slip employs a large particle kaolin intended for this purpose (e.g. Opticast). The flared lip works as expected, keeping the rim nice and round. No cracks have appeared at handle joins, even for pieces left in the mold overnight. The mold halves mate with each other very well and the seam is easy to remove. The seam on the base is an issue - I have to be careful to line up the halves well before clamping the mold strap - this is a warning for accuracy during the mold production stage. And the possible motive for a three-piece mold.

Context: AI-imagined mug I chose.., Coffee Mug Slip Casting..

Wednesday 10th April 2024

3D printed plaster filled case mold ready for pouring block mold

3D printed mug mold

This is part of a project to make a slip-casting mold for a coffee mug. In the slicer, I split the print into two pieces 22mm up from the base. This enabled doing the bottom section right side up and the top one upside down. That drastically cut the amount of support generated (and thus printing time). I scotch-taped the two halves together and filled it with plaster to produce a rigid block mold. The two halves fit so precisely it is difficult to tell where they join. The big benefit of printing it upright like this is that the all-important front face is very flat (there is some warpage on other parts but that does not matter).

Context: Coffee Mug Slip Casting..

Wednesday 20th March 2024

A better cone 6 oatmeal glaze using Ravenscrag Slip

Ravenscrag oatmeal glazed mug

Left: G3933EF oatmeal based on Ravenscrag Slip.
Right: G3933 oatmeal based on a mix of G2934 matte and G2926B glossy base glazes.
Both have the same added colorants. The Ravenscrag version features several advantages. Most importantly much less tendency to crawl. It has better application properties, the slurry needs less water and it is naturally thixotropic. It has an extra option for adjusting properties: Changing the ratio of roast-to-raw Ravenscrag clay. It is responsive to cooling differences - more matte on slow cool versions of the C6DHSC schedule (e.g. 150F/hr), more glossy on faster cools (e.g. 250F/hr). And, its recipe is adjustable (e.g. raising the MgO if a more persistent matte is needed). And, it looks and feels way better, interacting with dark bodies for richer color and varying in tone more for thinner and thicker sections.

Context: Ravenscrag Slip, Sometimes it is better..

Wednesday 13th March 2024

Use the same runny glaze as its own catch glaze

As runny glaze as its own catcher

This is G3948A, a super runny cone 6 iron red glaze. The clay body is M340. This glaze has to be runny, applied thickly enough, be held at temperature and cooled slowly to achieve this visual effect. When applied at the needed thickness it will run off the ware onto the kiln shelf during firing. Why has that not happened? A catcher glaze on the lower section. In this case, the catcher is the same glaze. On the left, the bottom half of the mug has just been dipped into the glaze quickly, giving a layer that is too thin to achieve the red effect. That dried within a few seconds and enabled pushing the top half down into the dipping glaze for twice as long (the inside has a liner glaze and is waxed up to the rim). The upper section glaze is guaranteed to run and the bottom is not thick enough to run. The result is complete blurring of the dividing line and coverage that looks natural and flawless.

Context: Stop a runny glaze.., Catch Glaze

Tuesday 5th March 2024

Paint another layer onto a fired glaze? Yes. With CMC gum.

The cone 6 mug on the left has the G3933A glaze, applied as a dipping glaze. It turned out poorly - crawling from corners and looking thin and washed out. I made a brushing glaze version of this (which adds 1.5% CMC gum), I keep it around for this very purpose. It has a high specific gravity (unlike commercial ones that have high water contents - they will run and go on too thin if you try this). Because of the gum it dries hard, there is no shrinkage or cracking. On a second firing, using the C6DHSC schedule again, (mug on the right) the surface is transformed - thicker, more vibrant color (being picked up from the underlying body).

Context: CMC Gum, Six layers 85 Alberta.., Control gel using Veegum.., Convert a pint of..

Wednesday 28th February 2024

Iron red glaze fired at cones 6, 5 and 4

Iron red glaze at cone 6, 5, 4

These mugs are Plainsman Coffee Clay. The glaze on all three is G3948A iron red. They were fired at cone 6, 5 and 4 using the C6DHSC schedule (adjusted for top temperature). As can be seen, the red color depends on the melt fluidity achieved at cone 6.

Context: Same glaze on black.., Iron Red Glaze

Sunday 25th February 2024

Finished cast v1 stoneware beer bottles

Cast ceramic beer bottles

The center bottle is a standard glass one, the other two are ceramic, cast out of the version 1 plaster mold. The stopper fits perfectly. The clay is Plainsman M370 + 10% raw umber, it fires black. The glaze is GA6-B. They were fired using the C6DHSC firing schedule. The slightly larger size will enable inserts at the bases to inlay a logo or other info. These bottles are a testament to how 3D printing and 3D design now make it possible for even casual potters to make pieces never before practical or even possible.

Context: Slip cast leather-hard full-sized.., Ceramic beer bottles with.., Beer Bottle Master Mold..

Saturday 24th February 2024

The incredible plasticity of bentonite. It is the secret to win the ThrowDown!

Two dissected vases showing the comparison in wall thickness

The 20cm vase on the left is thrown from what I thought was a very plastic body, M370. I achieved close to the same thickness top-to-bottom (5mm). The one on the right was the same original height, 20cm. But it has dried down to only 18cm high, it shrinks 14% (vs. 6% for the other). The thinnest part of the wall is near the bottom, only 2mm thick! How is it possible to throw that thin? The body is 50% ball clay and 50% bentonite. Bentonite, by itself, cannot be mixed with water, but dry-blended with fine-particled ball clay it can. That bentonite is what produces this magic plasticity. But it comes at a cost. It took about four days to dewater the slurry on our plaster table. And one month under cloth and plastic to dry it without cracks.

Context: Bentonite, Drying Ceramics Without Cracks.., Plasticity

Friday 23rd February 2024

Coarse body fires with smoother glaze

Glaze fires better on coarse body

On the left is Plainsman M332, a sandy and coarse body dry ground at 42 mesh. On the right on a wet-processed body, sieved at 80 mesh and then filter pressed - it is porcelain smooth. Yet that glaze, GA6-C, on the smooth body is covered with blister remnants while the same glaze on the coarse body is glassy smooth (they were in the same firing). That smooth glaze is courtesy of the C6DHSC slow cool firing schedule. But why does it perform so poorly on the finer body? That body is being overfired. Pieces are warping. Although not bloating, it is beginning to decompose and generate gases, they are producing the blisters.

Context: Melt flow test demonstrates.., Glaze Blisters

Tuesday 20th February 2024

Same glaze on black stoneware and white porcelain

The same glaze on black stoneware and porcelain

The glaze is G3948A iron red fired at cone 6 using the C6DHSC schedule. The bodies are Plainsman Coffee Clay and Polar Ice (the insides are different glazes). They were in the same kiln. These mugs demonstrate how much reactive glazes can interact with the body beneath and how much that affects their fired properties, especially when they have high melt fluidity like this one. On the left the glaze is drawing color out of the body. The porcelain on the right has no color to give but it does have sodium - and it is supplying enough to act as a catalyst to the creation of the iron crystals.

Context: Melt flow test demonstrates.., Iron red glaze fired.., Reactive Glazes, Body glaze Interface

Sunday 18th February 2024

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Plainsman Pottery Supply, 9517 - 41 Ave NW, EDMONTON, AB T6E 5X7
Phone: 780-440-4791, FAX: 780-490-7591, Email: larry@plainsmanclays.com