Important Notice

Plainsman Clays Ltd. will be closed to public access starting Thursday March 19. We will keep the doors closed (no exceptions), but continue to take and fill orders via phone (credit card only accepted) and e-mail. Pick up orders will be placed on at the front of the building, however we will be unable to assist in any loading. These measures allow us to limit contact with customers and minimize any risk with regards to the COVID-19 virus.

We can be reached by phone at 403-527-8535, fax 403-527-7508 and via email at plainsman@telus.net.

Thank you for your understanding during this difficult time.


CMC gum solutions can go bad

That is why glazes containing CMC often need a biocide if they are going to be stored for extended periods. We made this one. The gallon jar of Laguna gum solution sitting next to this did not go bad, that means they have added some sort of anti-microbial agent.

Context: CMC Gum, Micro Organisms

Sunday 24th May 2020

Trafficked online recipes waiting for a victim to try them!

A pile of printed recipes to try, but few are likely to work

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).

Context: Trafficking in Glaze Recipes, Metal leaching from ceramic glazes: Lab report example, Mechanism, Base Glaze, Limit Recipe, Glaze Recipes

Saturday 23rd May 2020

Metal leaching from ceramic glazes: Lab report example

Metal leaching from ceramic glazes: Lab report example

This lab is certified by the US Department of Environmental Protection (DEP) for drinking water and waste water analysis. They also provide pottery glaze leaching analyses (the water is kept in contact with the glaze then analysed for trace levels of specific metals). Each suspected metal to be tested for entails a separate charge ($30-60 in this case). That means that testing one glaze for several metals could cost $200. How to make sense of these numbers? Google the term: "heavy metals drinking water standards", and click "Images" to find charts with lots of data. Searching pages for this term will find books having detailed sections on each of the metals. Typically you are only interested on one metal in a specific glaze (often cobalt or manganese). There are ways to sleep better (about the likelihood your glazes are leaching metals) if you cannot do this: Do a simple GLLE test. And avoid the online trafficking in hazardous recipes. Better to find a quality base glaze (matte and transparent) that works well on your clay body. Then add colorants, opacifiers and variegators; but doing so in a conservative manner.

Context: Are Your Glazes Food Safe or are They Leachable?, Attack on Glass: Corrosion Attack Mechanisms, Having Your Glaze Tested for Toxic Metal Release, Glaze Leaching Test, Concentrate on One Good Glaze, Want bright orange? Use a stain in your own base transparent recipe., Trafficked online recipes waiting for a victim to try them!, USA DEP water testing info page, Chemical contaminants in drinking water, Brandywine Scientific Lab Website, Liner Glaze, Leaching

Wednesday 20th May 2020

Why it is not a good idea to use straight stain

Two ceramic mugs with a rubber-stamped logo using a stain/glycerine ink

The logo on the left was rubber-stamped using and ink mix made of only glycerine and Mason 6666 black stain. The glaze is shedding off during firing. Multiple properties needed by a stamping ink are not present here. First, the stain dries as a powder, it has no hardening or bonding properties, glycerine is its only mechanism. Second, it is too concentrated, the black color is so powerful that it bleeds excessively into the overlying glaze. Third, it does not melt during firing so it does not bond with the body below. And, it either develops only a fragile interface with the glaze above, or sheds it off. The piece on the right mixes the stain 50:50 with a glossy transparent glaze (having 20% kaolin), it lays down better, accepts the overglaze layer better (because it has less glycerine), presents less problems in handling before glazing and it has no issues with the overglaze crawling off during firing. Black stains are potent, a 75:25 stain:glaze mix would work even better.

Context: Silk screen mediums, Why you should not paint pure stain powders over glaze, Silk screen printing, Stain Medium

Friday 15th May 2020

The same raw material, same temperature, different batches!

Test bars of three different batches of PV Clay (a plastic feldspar) fired at cone 8 (porosity is shown). This is how much a manufactured material can vary, obviously body blenders need to be watching the properties of the materials they receive. This raw material is employed in many clay bodies in North America as a plastic flux. The chemistry and physical properties of this material can be duplicated with a blend of kaolin, feldspar and silica.

Context: PV Clay

Tuesday 12th May 2020

Making your own plaster bats is easier than you might think

A rubber mold for making plaster bats

The cost of plaster bats prevents many from buying them. But that is a non-issue if you make your own. Using this rubber mold I have just made 8 - 12" bats and I still have 20 lbs of plaster left in the bag! The first rule for a good result: Lay it on a level level table (so the bat does not come out thicker on one side than the other). I just just weigh 1600 grams plaster, dump it in 1120 grams of water, wait 4 minutes, mix 4 minutes and pour. As soon as the water at the top disappears I dump the next batch of plaster in the water and repeat (by the time the next plaster is ready to pour I can remove the last bat from the mold). You can buy one of these rubber molds at Plainsman Clays for $75 plus shipping. Or, there are many ways you can make your own mold.

Context: Why throw on a plaster bat when making larger pieces?, BatMate plaster bat gripper, Plaster bats are indispensable to the potter, Plaster Bat

Monday 11th May 2020

Why throw on a plaster bat when making larger pieces?

A large thrown vessel, having dried overnight under plastic and on a plaster bat, is ready to turn o

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.

Context: Drying Ceramics Without Cracks, Wanna throw porcelain plates with thick bottoms and thin rims?, Making your own plaster bats is easier than you might think, Plaster Bat

Monday 11th May 2020

Want bright orange? Use a stain in your own base transparent recipe.

Fired glaze tiles showing an orange promise, what actually came out and a better way

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.

Context: Trafficking in Glaze Recipes, Metal leaching from ceramic glazes: Lab report example, Encapsulated Stains

Thursday 7th May 2020

It's possible to formulate a porcelaineous stoneware with just two materials

Two clear glaze cups show the color and glaze fit differences between feldspar and kaolin

Left: 65% #6Tile kaolin and 35% nepheline syenite. It's white but crazes the glaze and has 1% fired porosity (measured in the SHAB test). Thus it does not have porcelain density. Plasticity is very good. Right: 65% M23 Old Hickory ball clay and 35% nepheline syenite. The glaze fits, the body has zero porosity (very dense) and plasticity is fantastic! The body on the left needs a 20% silica addition (to stop crazing) and 5% more nepheline (to reduce porosity to porcelain levels). But the remaining 40% kaolin will not be nearly enough for a workable plasticity (so bentonite will be needed). The body on the right does not need fixing, it works beautifully as is. Ball clay is easier to flux with feldspar and it contains its own natural silica.

Context: Ball Clay, Stoneware, Porcelaineous Stoneware

Thursday 7th May 2020

Melt fluidity differences are not obvious by just comparing glazed ware

The glaze on two porcelain mugs looks the same, but the melt flow is very different

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.

Context: G2934Y, G2934Y variations for fired hardness, COE adjustment, etc, Melt Fluidity

Wednesday 6th May 2020