Mother Nature's stoneware and glazes!

To make these cone 6 mugs I slake and slurry up raw lump Plainsman MNS clay and process it through a 325 mesh vibrating sieve. This natural porcelain vitrifies to zero porosity at cone 6, yielding incredibly strong ware. I also make these outside and inside glazes, GA6-C and GA6-B, from clays we mine in Montana and Alberta. Using glaze chemistry I can maximize the clay percentage to more than 70% of the recipe (for firing at 2200F). Of all the pieces I make, ones like these mean the most to me.

Related Pictures

Mother Nature's porcelain - From a Cretaceous dust storm!

During a 6 week of mining in 2018 in Ravenscrag, Saskatchewan we extracted marine sediment layers of the late Cretaceous period. The center portion of the "B layer", as we call it, is so fine that it may have been wind-transported (impossibly smooth, like a body that is pure terra sigillata)! The feldspar and silica are built-in, producing the glassiest body surface I have ever seen, starting at cone 4 and lasting to cone 8. Despite this, pieces are not warping in the firings! I have not glazed the outside of this mug for demo purposes. I got away with it this time because the Ravenscrag clear glaze GR6-A is very compatible (the thermal expansion is high enough to avoid glaze compression issues and low enough not to craze). With other less compatible glazes these mugs cracked when I poured in hot coffee. To make this body I am slurrying it up as a slip and processing it to 325 mesh (using a vibrating sieve).

Incredible Mother Nature’s porcelain

A hand-built mug made from 100% of a naturally occurring porcelain

This is made from 100% of a natural clay (3B) from the Whitemud formation in Ravenscrag, Saskatchewan. To make this body, which I call MNP, I slake and slurry up the raw clay lumps, sieve it to 200 mesh and then dewater on a plaster table. I rolled the plastic clay into a thin layer, cut it into a cross-shape using a 3D printed cookie-cutter, drape-molded it over a plaster form and then slip-joined the seams. It fires very dense and strong (to zero porosity like glass!). It holds together well and joins well with its own slip. Although not super plastic, it is smooth and fine-grained like a commercial porcelain body. I add 1-2% bentonite to make it more plastic when needed. It can be rolled extremely thin and yet does not warp in the firing! This mug has a weight-to-volume ratio of 2.08 (the weight of water it will hold compared to its own weight).

Testing your own native clays is easier than you think

Some simple equipment is all you need. You can do practical tests to characterize a local clay in your own studio or workshop (e.g. our SHAB test, DFAC test, SIEV test, LDW test). You need a gram scale (preferably accurate to 0.01g) and a set of callipers (check Amazon.com). Some metal sieves (search "Tyler Sieves" on Ebay). A stamp to mark samples with code and specimen numbers. A plaster table or slab. A propeller mixer. And, of course, a test kiln. And you need a place to put all the measurement data collected and learn from it (e.g. an account at insight-live.com).

Links

Projects	Evaluating a clay's suitability for use in pottery Would you like to be able to use your own found-clays in your production? Follow me as we evaluate a mystery clay sample provided by a potter who wants to do this.

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