• Materials for Ceramics

3B Clay

Alternate Names: B, PR#3 B, B clay

Description: Buff firing highly vitreous, plastic, very smooth stoneware clay

Notes

A buff firing stoneware clay that densifies to zero porosity around cone 6 (or below). It is mined at Ravenscrag, Saskatchewan, Canada by Plainsman Clays. It is part of the Whitemud formation. It has pottery plasticity (suitable on a potter's wheel) and is exceptionally smooth, even without processing. It makes up a significant percentage of many of the bodies produced by Plainsman Clays.

Online you might see this referred to as MNP (Mother Nature's Porcelain), this is a reference to its smooth and vitreous nature (rather than fired color) and its extreme stability when fired to temperatures far higher than its initial vitrification range. These properties also make it an ideal base for making engobes and underglazes.

This material can be synthesized using a 60:40 mix of ball clay and nepheline syenite or feldspar. Tune the degree of fired maturity by adjusting that ratio.

There is some arguments about whether the mineralogy of 3B should be muscovite or illite. Here is the comment of one technician: "With regards to illite or muscovite, the only way to categorically differentiate between the two is to determine the layer charge (most easily by electron microscopy) which I didn't do. In this sample, the mica component has no detectable expandability which suggests a high-charge mica with very little depotassification typical of muscovites. Also, the x-ray scattering domain size is quite large with minimal disorder which you seldom find in illite but expected for muscovite. However, the kaolinite in the sample is extremely fine as one would see in fireclays. 41% quartz in the sample is accurate. You can easily verify this from your chemistry by checking the contributions of muscovite, kaolinite, smectite and K-spar to the total SiO₂, and constraining potassium to muscovite and K-spar, and Mg to smectite. From my experience, a high plasticity and the apparent illitic properties that you see in the clay is most likely due to the discrete smectite content (8%). Note that the activity of smectite is several orders of magnitude (up to 10 times) greater than the finest kaolinite or illite."

Major trace elements:
424 Ba ppm
34 Sr pmm
24 Y ppm
10 Sc ppm
249 Zr ppm
1 Be ppm
65 V ppm

Related Information

Plainsman 3B fired bars

These show it to be very vitreous, reaching zero porosity shortly after cone 4. It is also very stable in firing, not melting or bloating all the way to cone 10. This is the raw slaked material so iron specks are visible, these blossom in reduction firing.

Mel Noble at Plainsman Clay's Ravenscrag, Saskatchewan quarry

Plainsman Clays extracts 6 different sedimentary clays from this quarry (Mel knows where the layers separate). The dried test bars on the right show them (top to bottom). The range of properties exhibited is astounding. The top-most layer, A1, is the most plastic and has the most iron concretion particles (used in our most speckled reduction bodies). The bottom one, 3D, is the least plastic and most silty (the base for Ravenscrag Slip). The middle two, A3 and 3B, are complete buff stonewares (e.g. M340 and H550). A2, the second one down, is a ball clay (similar to commercial products), it is refractory and the base for Plainsman Fireclay. The second from the bottom, 3C. fires the whitest and is the most refractory (it is the base for H441G).

When a DIY black underglaze makes sense

Black brushwork needs to go on thick enough in one brushstroke. Commercial products we have don't do that - thus my motivation to work on this. Another issue is that they try to cover too wide a firing range (thus they melt too much at the high end and not enough at the low end). I am experimenting on cone 6 Polar Ice porcelain jiggered bowls using G2926B dipping glaze. The base underglaze recipe here is a 90:10 MNP:nepheline syenite mix (you could use your own porcelain instead of MNP and feldspar instead of nepheline). To that, I add 15% black stain, 1.5% CMC gum and 5% bentonite. With the CMC gum and bentonite, and blender mixing, a brushable consistency that stays put can be achieved at a fairly low water content compared to commercial products (enabling it to go on thicker in a single brush stroke). Assuming application at leather hard state, the drying and firing shrinkage can be matched to the body by varying the plasticity of the porcelain used (e.g. the percentage of bentonite it contains). And the percentage of stain can be tuned for enough color but no bleeding, bubble clouding or crystallization. And we can adjust the degree of maturity by varying the proportions of MNP and Nepheline (commercial underglazes often melt too much by cone 6 and fade and diffuse as a result), this one stays opaque black.

Underglazes suitable for making silk screen transfers are another special case. The ideal one needs to cover well like this one. But it also needs to gel and harden enough to hang onto the paper but not so hard that it does not separate and transfer to the ware. Commercial products for brushing are unlikely to be optimal so it makes sense to mix your own and experiment with different amounts of gum.

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).

Calculating the highest % of 3B clay to create a glaze recipe

In this screenshot, Plainsman 3B is being using to source almost all of the Al₂O₃ needed by the recipe (to match our standard cone 10R transparent G1947U). The KNaO is being sourced from the frit rather than feldspar (since it has almost no Al₂O₃). Only silica and calcium carbonate are needed to round out the rest (plus the zinc).

Incredible Mother Nature’s 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).

Ravenscrag Saskatchewan clays fired at cone 10R

Glazeless (top) and with glaze (bottom): A1 (bentonitic), A2 (ball clay), A3 (stoneware), 3B (porcelains), 3C (lignitic ball clay), 3D (silt). The bottom row has also shows soluble salts (SOLU test).

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