Here is why new grinding equipment is a really good idea

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.

Related Pictures

An All-Canadian Fine Ball Clay is in Sight!

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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!

Plainsman Ravenscrag Quarry in 2025:

It is Getting Complicated

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This has served the company for almost 50 years. The grinding plant, which has also served 50 years, has been able to process these clays to 20 and 42 mesh. While this quarry has been a key advantage for the company and coarsely ground bodies still sell well, the demand for smoother, more plastic and whiter bodies has seen a steady trend to the use of more and more imported 200 mesh powders (eg. clays, feldspar, silica) to make bodies. The star clay in the quarry is 3B, it is smooth and contains natural feldspar. Minings are typically done now just to get it. But because it is near the bottom (there are 6 layers plus overburden), others continue to bloat the inventory of unneeded materials (some of these piles are 30+ years old). On the next mining, the cost of stockpiling the overlying layers vs discarding them will have to be rationalized.

Most of these piles (especially the ball clay) could be sold on the open market if 200 mesh grinding was possible. The most serious problem is the amount of overburden that must be removed. Perhaps even more serious, since other clays are not needed, the 3B has to bear the entire cost of the mining. Now that better, more accessible and easier to mine clays further east have been found, the way forward is looking much better. In fact, it looks so promising (with testing of course) that it could be time to begin reclaiming this site.

This quarry has one saving grace: The bottom layer, which has been left in the ground the last two minings, 3D. It is the clean (low in contaminants) and, like 3B, contains natural feldspar. But it is not plastic, its usefulness depends on a better quality ball clay.

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