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These two Plainsman M370 mugs were fired at cone 6, the left one with G2934 matte glaze, the right one with G2934Y4 matte. They look and feel identical in the hand. The two glazes have the same chemistry. But they employ different materials to source that chemistry. The secret of of the matteness is high MgO (magnesia content). In the glaze on the left that MgO is sourced by dolomite, a lot of it. The glaze on the right sources it from a special frit, Ferro 3249. The impact of this difference is visible in the melt flows, the fritted one is obviously melting and flowing better. On other clays, especially stonewares, the G2934 can have a dry surface that cutlery marks. Thicker applications make it worse. But the Y version exhibits no such issues. Its mattness, durability, cleanability and hardness are so good that it is being used in floor tile.
Friday 29th May 2020
A lot of ceramic manufacturing companies have come and gone in this city since 1889. An amazing company of the time was Alberta Clay Products. They made vitrified clay pipe and had around 20 huge beehive kilns. But in 1962 something terrible happened: Their factory burned to the ground! But a year later something good happened: Luke Lindoe used one of their buildings to start Plainsman Clays. For fifty six years, operating longer than any of its predecessors, Plainsman Clays has manufactured clay bodies using the same clay resources that ACP and others in the area used. While it may appear that Plainsman is the only manufacturer left, that is not exactly true. Lots of potters produce stoneware and porcelain in this area, and across Canada, using products we manufacture and supplies we distribute.
Tuesday 26th May 2020
Polar Ice is made by Plainsman Clays, it is by far the most expensive body they make (because of the use of New Zealand kaolin and VeeGum). I call these my "sunshine mugs". They are fired at cone 6 (2200F) with a transparent glaze on the inside (G2926B) and G2934Y yellow silky matte on the outside. This yellow glaze showcases the translucency in sunlight better than any other I have seen. The high plasticity and this "pie crust" method of making them enables thinner walls than any other method I know of, even casting. Although the walls of this piece are about 3.5 mm thick, I have achieved 2 mm using stiffer clay! Even with very thin walls the weight of the handle does not pull the lips of these into an oval-shape.
Tuesday 26th May 2020
You found some recipes. Their photos looked great, you bought $500 of materials to try them, but none worked! Why? Consider these recipes. Many have 50+% feldspar/Cornwall/nepheline (with little dolomite or talc to counteract their high thermal expansion, they will craze). Many are high in Gerstley Borate (it will turn the slurry into a bucket of jelly, cause crawling). Others waste high percentages of expensive tin, lithium and cobalt in crappy base recipes. Metal carbonates in some encourage blistering. Some melt too much and run onto the kiln shelf. Some contain almost no clay (they will settle like a rock in the bucket). A better way? Find, or develop, fritted, stable base transparent glossy and matte base recipes that fit your body, have good slurry properties, resist leaching and cutlery marking. Identify the mechanisms (colorants, opacifiers and variegators) in a recipe you want to try and transplant these into your own base (or mix of bases). And use stains for color (instead of metal oxides).
Saturday 23rd May 2020
The Plainsman Clays factory is right beside a baseball park. A beautiful place in the summer where children play and teams compete. But in the afternoon and evenings the deer move in. And mow the grass! The deer stay around all winter, in this residential area they are away from the coyotes and occasional mountain lion in the nearby river valleys.
Context: Plainsman Clays
Sunday 17th May 2020
Different depths are available, you need the 0.047 maximum relief depth (you can order a sample pack to try the various types they have). While shallower ones will make a crisp design into the clay, if you wish to put color into the recesses (at bisque stage) the shallow depth will make it difficult to avoid sponging it out when cleaning the high spots. Traditionally polymer plates have had metal backing and were expensive (and brittle). But these are flexible, inexpensive and easy to get online. When designing them create a border around the outside (when the stamp is pressed hard into the clay, the edges smear outward, that containment-line keeps edges clean). Also, the plates do not actually need to be stuck to a piece of wood, it is often better to lay them face down on the clay and use a wooden block and hammer to press them into the clay (which need to be quite stiff). Use spray cooking oil as a parting agent if needed.
Friday 15th May 2020
These mugs are on a plaster table, just thrown on the wheel. I made the box cover from a large sheet of cardboard and painted wax emulsion on the inside. I drew a line on the plaster for its boundaries. When left overnight under the box the mugs dewater evenly, the plaster pulls water from the air in the box and directly from the thicker bases. In the morning they are stiff enough for handle attachment and to turn over on an arborite bat for a little more drying to ready them for trimming. An big advantage of this method is that I can throw ware minutes before closing time, come back in the morning, and they are ready. And they do not experience the unevenness in drying that normally happens when pieces are left to air dry (after throwing) until they are stiff enough to support a cloth and plastic to cover them.
Context: Drying Ceramics Without Cracks
Thursday 14th May 2020
To achieve more even drying. As soon as was practical after throwing (a few hours), I covered the piece with a cloth and then put a garbage bag over it. While that put the upper section a little ahead of the base in drying, over night the base caught up (the plaster sucks the water out of it, even the walls of the piece stiffen). In the morning I remove the plastic and within an hour or two it is ready to lift off the bat and turn over, shortly after that I can trim it. I secure each plaster bat to the wheel-head using a "Batmate", that works extremely well. To stick the clay to the plaster well I apply a thin layer of slip, round off the piece of clay and firmly slam it down onto the plaster (if it is not rounded it will not stick as well or may break the bat). This is quick and effective to achieve the even drying needed to avoid a drying crack. This method is especially important for large plates and bowls, which often suffer s-cracks.
Monday 11th May 2020
Orange is a very difficult color in ceramics. Inclusion stains are the only reliable method, they universally used in industry. But you could ignore that and try a bunch of recipes online. When they are presented on flashy web pages they can look tantalizing. But beware! Are the exotic materials you need to buy worth it. Will it actually fire orange? Will it craze or run or blister or leach or cutlery mark or crawl or settle like a rock in the bucket? It is much better to put an orange encapsulated stain into a transparent glaze you already know works on your clay. Then just experiment with percentage to get the color you want. Or, how about trying a premixed orange at low fire? Ware can be amazingly functional at low temperatures (e.g. cone 03-02) and bright colours labelled for cone 06 mostly work fine in that range.
Thursday 7th May 2020
This is 70% kaolin and 30% feldspar. Fired at cone 6 with glaze G2926B. The fired body has a nice porcelaneous surface. But, right out of the kiln, it crazes like this! The dense craze pattern indicates a very serious fit problem. The thermal expansion of the kaolin:feldspar mix is much too low. Adding 25% low-expansion silica will solve the problem. The other issue is with the flat particle shape of kaolin. The throwing process has lined up the predominant kaolin particles concentric to the centre. During drying, and especially firing, more shrinkage occurs across them than along them. All ten of the cups made cracked like this! The solution is adding a filler, one with rounded particles to separate the kaolin plates. Silica is perfect, using the same 25% addition. The grains act like aggregate in concrete, strengthening the matrix and separating the clay particles, forcing them to orient more randomly.
Wednesday 6th May 2020
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