These two unglazed pieces are made from the same clay, M340. They are fired at the same temperature. But the one on the right has 1% talc added. Greying of the color is a characteristic visual change as this clay body transitions into the vitreous state we target. That transition happens over a narrow temperature range. Because the raw materials naturally vary in the temperature at which they vitrify, we have to tune the recipe so that the transition happens from cone 5 to cone 6. It is accompanied by a drop in porosity of 2% or more (according to our SHAB test). Talc acts as a catalyst for this change; in this case, only 1% is needed. By itself, talc is refractory. Yet it acts as a flux here! The fact that it can effect this big of a change with only 1% is amazing. Interestingly, this phenomenon only occurs with tiny talc additions.

The materials to make M340 travel 200km to get to our plant (from Ravenscrag, SK).
M370 is a different story. The kaolin (from Georgia) travels 3700km, the nepheline (from Ontario) travels 3100km, the silica (from Illinois) travels 2300km, the ball clay (from Tennessee) travels 2800km and the bentonite (from Wyoming) travels 1000km. Weighting each material distance by its percentage in the recipe calculates to 2900 clay-kilometres! Thus, all the boxes of M370 we make in a year travel about 60,000,000 km, enough to go to the moon and back 50+ times! This realization brings renewed motivation to develop new clay deposits, ones that are white enough to make an M370-like body and which are only 400km away. Until then, you can cut the mileage now: Use an engobe on M340 and make it whiter than M370 (and darker than Coffee clay).

These two pieces have been fired to cone 6, without glaze, I use this as a way of comparing changes in the character of the fired surface over time. These are made from a mix of A3 and 3B, our two main raw stoneware clays. The mix has been ground to 42 mesh (using our hammer mill). These materials vary in the amount of sand they contain and the amount of iron stone concretion particulates, so we will also see smoother and more speckle-free than this as a matter of normal variation. We have made sandy and speckled clays like this for so long that they seem normal to me. Yes, rustic bodies do have their appeal. However, the limits of our particle size reduction equipment and current quarry materials have resulted in importing American materials to satisfy customers who want smoother, whiter, more plastic and more vitreous bodies. We are now producing tens of thousands of boxes a year made from these imported materials! Transporting expensive clays at great distances begs the question of why we have not better leveraged the clay resources that are right here. That, and associated independence, quality and lower production costs, are coming soon.

Six different sedimentary clays are extracted from this quarry. It was opened in the 1970s, the best location available at the time. These test bars were made by slaking select lumps from each layer (thus exhibiting their best performance). The left-most dried test bars show the layers (top to bottom). The A1 top layer is the most plastic and has the most iron contamination (it is used in our most speckled reduction firing bodies). A2, the second one down, is a ball clay (similar to commercial products, although darker burning), it is very refractory and the base for Plainsman Fireclay. A3, third from top, is a complete buff high-temperature stoneware (like H550), although sandy and over-mature at cone 10. 3B, third from bottom, is a smooth medium-temperature stoneware; it contains significant natural feldspar (although fired color and particulate contamination are the most variable). The second from the bottom, 3C. fires the whitest and is the most refractory (it is the base for H441G). The bottom one, 3D, the best product in the quarry. Although the least plastic and most silty, it is also very fine particled and the cleanest (consistently free of particulate impurities and sand), it pairs very well with a ball clay to make a cone 6 stoneware.

On the right is Plainsman A2 ball clay with 35% nepheline syenite added to vitrify it around cone 6 (these bars are fired at cone 2, 4, 5, 6 and 7 - top to bottom). Using our grinding equipment, we can process it to 42 mesh, as we have done since the 1970s. On the left is a Flintoft ball clay (cone 10R top and 10, 9, 8, etc - top to bottom). But this is the raw material, just slaked (not ground). It reaches zero porosity at cone 6 without a feldspar addition (because Mother Nature has added it for us). And the plasticity? This ball clay dry shrinks 9%, it is super plastic, much more than the A2/feldspar mix. While nearby deposits also contain refractory ball clays, this one is truly something special. It enables not just highly plastic vitreous stonewares but it fires white enough to be a potential ingredient in an All-Canadian plastic cone 6 porcelain. In an unexpected turn of events, we now have the opportunity to get this clay in a way that is much easier than expected. We have tested mixing this with PR3D, the best material in our Ravenscrag quarry - together the two can make killer clay bodies!

The clay is Plainsman 3B.
Left: Without processing, other than grinding to 42 mesh (currently the finest we can grind on a practical scale), if fired toward zero porosity it burns like this (at cone 6, 8, 9, 10 and 10R bottom to top). Of course, this material is mainly used in non-vitreous bodies at cone 6, so these are not issues. The speckle and bloating are caused by impurity iron-bearing particles and others having an LOI (they decompose and produce gases that cause the bloats).
Right: The impurity particles make up a small percentage, they can be removed in our lab by sieving to produce a natural porcelain that fully vitrifies by cone 6 (the middle bar). Only about 5% of the material was removed to produce this amazing product (we call it MNP).
Imagine what could be done if we were able to mine raw material further east, where clay quality is much better!

This is kaolinized sand from Flintoft, Saskatchewan. It is among clays we are currently rediscovering. This is far more plastic and fires much whiter than our Ravenscrag quarry equivalent. Consider highlights of physical tests to characterize it (data shown lower left):
-Super refractory (thus theoretically pure). The SHAB test bars (lower right from cone 10R and 10 down to 6 oxidation) correspond to the SHAB test results in the chart. Even at cone 10, this has an amazing 19% porosity. With almost zero shrinkage.
-Plasticity: Excellent (notice the texture of the plastic material in the close-up photo on the upper left).
-The DFAC test disk upper right shows perfect drying performance and very low soluble salts.
-White burning: The top bar is reduction-fired yet barely darker than the one below it at the same temperature in oxidation (indicating low iron content).
-Centre-bottom: G1947U clear glaze on it fired at cone 10R.
-Easy-to-access in new and old quarry sites.
I compared this with about 10 other clays in the area, doing the same for all of them, preserving a treasure trove of data for clays we have been overlooking.

An update of the book "Clay Resources of Saskatchewan". The cover photo is titled "Kaolinized sand of the Whitemud Formation". The writers are lamenting the underutilization of this resource and almost pleading for industry to recognize its value! The cover shows the mining face at the historic Claybank brick plant. This clay is far whiter than what Painsman Clays mines at Ravenscrag, Sask (about 250km west of this). This site was mined from the 1800s to 1970s. Bricks were made in half a dozen large beehive kilns and, even though reduction-fired with gas, they burned far too white. The company increased reduction to the point that soot formed on the bricks to darken the color and turn them brown!

We are finally listening and rediscovering how much whiter and more pure clays are further east in Saskatchewan (compared to our current mining site in the west). This hill is kaolinized sand, that sand can be removed to produce a Canadian raw kaolin that could replace much the hundreds of thousands of tons that are currently imported each year from Georgia, USA.

This one is saying: "I am the whitest kaolin in Saskatchewan. And, I am so plastic that even though I am mixed with 50% sand, I can be modelled and formed with no problem. Just remove the sand and you will have a world-class kaolin that is Canadian". W. G. Worster, called these kaolinized sands, which can be found in south central part of the province, "splendid". This outcrop is in Halbrite, a small town southeast of Weyburn. There are lots of other deposits, especially in the Wood Mountain, Flintoft and Claybank area that are also much whiter than anything we currently can get in Ravenscrag. But this one is king so far. Should we keep importing from Georgia or develop our own Canadian kaolin?

This is at the Whitemud Resources metakaolin (MK) site midway between Scout Lake and Wood Mountain, Saskatchewan. They mine ore that is separated into kaolin (reject material is silica sand) then dehydroxylated into metakaolin; an SCM (Supplementary Cementing Material), MK itself is a natural aluminosilicate pozzolan. They have a giant plant (the dome is big enough to play soccer in) and are capable of processing an order of magnitude more than we can. The mining face in their quarry appears to have the same layers that we mine in Ravenscrag. But, there are very fortunate differences:
-This deposit is near Flintoft, these clays will be much purer and whiter than what we can get in our Ravenscrag quarry (pending testing, of course).
-We need what is above the coal seam, they need what is below (their garbage is our gold).
-The layers appear to be the same as those in our existing quarry.
-Their grinding plant is capable of micron-sizes and is gigantic.
-Their by-product is silica sand!
-They are working on a mining plan for August extraction.
This is close to a "marriage made in heaven", we shall see. It is certainly going in the direction of enabling us to improve product quality. And hopefully, soon make an all-Canadian porcelain.

It has been five years since getting and testing samples of an amazing porcelain-like, clean-burning, highly plastic middle-temperature stoneware raw material from south central Saskatchewan. It is far superior to anything we have now. But, due to mix-ups, it appeared its location had been lost! But coming here to search again has turned up new information and I am quite certain this is the site (at Flintoft, Saskatchewan). Seeing and walking it has confirmed, contrary to the information we had, that the site is highly suitable for extraction (previous mine workings to the left are not shown). And, it is not the only site in the area. The Whitemud clays here are quite different from those in our Ravenscrag quarry, they are so good they obsolete almost everything we have (except perhaps PR3D). On seeing the range and quality, I am beyond excited! There are a lot of ducks that have to be lined up to be able to actually extract from a site like this, but the location has a lot of advantages. The current economic realities will be a powerful motivator to developing Canadian clay sources.

This in on display at the visitor center of the Grasslands National Park in Val Marie, Saskatchewan. Perhaps ones like this formed part of the inspiration Luke Lindoe had when conceiving of the logo for the company he would form. To us, this area is "clay country", but to tourists it is a place to see the living prairie and also history like dinosaur fossils, the mass extinction boundary, hearth sites, tipi rings, bison drive lanes, and cellar depressions.

This jigger mold-making method features a hybrid plaster form of the outside profile attached to a 3D-printed clamping baseplate. Clamp-on rails enable easy setup and extraction for mold production. Here are the steps:
-Download the drawing, edit the bowl profile and size (and the template) and then 3D-print the parts (typically using PLA filament). Print two rails.
-3D-print threaded anchors and attach them to the base plate.
-Center and clamp the spacer ring onto the flat side of the base plate.
-Set the model mold on a level surface, pour plaster into it (right to the rim), place the base plate (anchors down) onto it (being sure it seats down into the spacer ring to assure centering). The plaster should overflow up the air holes in the plate. Weigh it down and leave to set.
-Remove the mold (using heat gun if needed), finish the surface of the plaster (with a metal rib or 3D-print one with curves to match the contour) and soap it in preparation for pouring a working mold.
-Clamp the rails down to the base plate (using paper clamps), place the mold on a perfectly level surface and fill with plaster.
-Fit the template to your jigger arm (more than one cycle of editing the upper section and adjusting hole placement will likely be needed, so don't print it solid right away).
You now have a working jigger mold for use on a Giffin grip. Repeat the last step as many times as needed.

Many people suffer high-percentage Gerstley Borate "bucket-of-jelly" raku recipes they find online. Most of these are just transparent base recipes to which colorants are added. After years they found ways to tolerate this strange bedfellow. Now, a more normal material, Gillespie Borate, seems odd and is causing issues in the alternate reality "Ghastly Borate ecosystem". There is a better way. A frit is perfect for this application, Ferro Frit 3110 (or Fusion frit F-75). All it needs is 15% kaolin (e.g. EPK) to produce and easy-to-use recipe that is guaranteed to craze. The degree to which it crazes can be adjusted by trading off some of it for Ferro Frit 3249. We have assigned it a code number of L4264, a raku base transparent recipe. We have also catalogued some common recipes that people use and outlined the issues they have: L4264A, L4264B, L4264C, L4264D. Do you need a white? It is a simple matter of adding 10% Zircopax to this.

Reactive glazes (melt-mobile, crystallizing or heavily pigmented) are the least suitable for food surfaces because they have the potential to leach metals. Liner glazing ware is an excellent way to deal with this problem. Not only does this approach improve functionality but it can be aesthetically pleasing and practical in production.

This liner is GA6-B, a pottery glaze recipe we promote with confidence. Not only is it less likely to be leaching metals but also less likely to craze - this assures water tightness on non-vitreous bodies and eliminates any potential for bacteria growth in the cracks (especially if the body has porosity). Unfortunately, glazes that leach are also likely to stain and cutlery mark - these add more reasons why they are most often unsuitable for food surfaces.

The straightness of the dividing line is affected by both the application technique and the degree to which the two glazes bleed into each other and run. Read and watch our liner glazing step-by-step and liner glazing video for details on how to do this - it is practical for any potter or hobbyist (or even in production). And tap/click the picture above for other examples of this.