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We are one of about 90 ceramic suppliers in North America. But unlike almost all of them, we make most of our products from clays we mine and process ourselves. We intend to leverage this advantage to achieve the unmatched quality, assurance of supply and low prices this enables.

Technical Tips Blog

Amaco PC-20 vs Ravenscrag Floating blue

Ravenscrag Floating blue vs PC-20

G2917, which I mixed as a brushing glaze, is on the right. This is not sold in jars, I make my own labels as part of the demonstration that it is possible to make your own brushing glazes (ink-jetted onto regular paper, cut 62mm wide (2 7/16") and held securely on with 2 7/8" transparent packing tape). This glaze is less runny but lacks some of the floating white colouration. But that can be achieved using Alberta Slip floating blue L4655, it employs titanium instead of rutile (and relies on the rutile/iron mechanism for the blue color).

Context: Titanium instead of rutile.., Here is my setup.., Brushing Glaze, FLB

Tuesday 11th February 2025

Marbling stained porcelains - Watch out for firing shrinkage differences

A multicolored marbled porcelain bowl has cracked at the boundary between red and green

Stains can and do influence the degree of vitrification of a porcelain. Some stains will make a porcelain more refractory (decreasing fired shrinkage), others will make it more vitreous (increasing the firing shrinkage). Obviously, the greater the percentage of stain the greater the effect. Stained porcelains having differing fired shrinkages will stress at boundaries in accordance with the degree of difference in their fired shrinkages. In this piece, you can see how the boundary between the red (more vitreous) and green (less vitreous) porcelains is the point-of-failure. The only solution is to adjust the porcelain recipe to move the fired maturity in a direction that counterbalances the effect of the stain. For example, you could employ three recipes (regular, more vitreous, less vitreous) and use the indicated one for each stain added.

Context: Marbling, Firing Shrinkage

Monday 10th February 2025

Stained engobes can be applied thinly yet fire opaque

A black engobed leather hard mug

This black engobe, L3954F, is on a cone 6 buff stoneware (at leather hard stage). It contains only 7.5% Mason 6600 black stain. How is that possible? Why do people add so much more to their underglazes? Because this recipe has been tuned to have the same degree of maturity as the body - it therefore fires totally opaque. This contrasts with underglaze/engobe recipes containing significant frit, among other issues, their vitreous nature renders them translucent. Thus, up to 40% stain is needed to crowbar their opacity enough to intensify color. And a thicker application (that carries other issues).

Notice how thinly and evenly this is applied. This was possible because of another key factor: The slurry was adjusted to be thixotropic. The thinner layer enables drying more quickly. The body-compatible engobe recipe also means fewer issues with flaking during drying, better fire-fit.

Context: Absolutely jet-black cone 6.., The best way to.., Engobe

Thursday 23rd January 2025

Pure feldspar applied as a glaze: Possible because of the magic of thixotropy.

Suspending feldspar in water

These are pure Custer feldspar and Nepheline Syenite. The coverage is perfectly even on both. No drips. Yet no clay is present. The secret? Epsom salts. I slurried the two powders in water until the flow was like heavy cream. I added more water to thin and then started adding the Epsom salts (powdered). After only a pinch or two, they both gelled. Then I added more water and more Epsom salts until they thickened again and gelled even better. The result is a thixotropic slurry. They both applied beautifully to these porcelains. The gelled consistency prevented them from settling in seconds to a hard layer on the bucket bottom. Could you do this with pure silica? Yes! The lesson: If these will suspend by gelling with Epsom salts then any glaze will. You never need to tolerate settling or uneven coverage for single-layer dip-glazing again!

Context: Epsom Salts, Suspending pure feldspar and.., Craze city Feldspar and.., See the magic of.., Thixotropy, Powdering Cracking and Settling..

Tuesday 21st January 2025

Can you actually throw a Gerstley Borate glaze? Yes!

A thrown vase made of a Gerstley Borate glaze

G2931 Worthington Clear is a popular low to medium-fire transparent glaze recipe. It contains 55% Gerstley Borate (GB) plus 30% kaolin (GB melts at a very low temperature). GB is also very plastic, like a clay. I have thrown a pot from this glaze recipe! This explains why high Gerstley Borate glazes often dry so slowly and shrink and crack during drying. When recipes also contain a plastic clay like this one the shrinkage is even worse. GB is also slightly soluble, over time it gels glaze slurries even in smaller percentages. Countless potters struggle with Gerstley Borate recipes.

Context: Gerstley Borate, Gillespie Borate, Gerstley Borate 5 3.., Gerstley Borate vs Frit.., Replacing the Gerstley Borate.., Glaze Gelling, Plasticity

Wednesday 15th January 2025

Closeup of the polygon surface of a cast mug

Freshly slip cast mugs

This is L4023F (a test body like our H440 cone 10R body). The polygons on this surface are produced when the 3D CAD software converts from its native format to an STL file that slicer software can use. These are the product of the default settings (which can be changed but increase file size). The precision of the 3D printer is evident in that it can reproduce these. Since the polygons are not visible in the final glazed piece, neither the PLA surface on the 3D printed block mold, or the surface of the plaster case mold made from it, were sanded.

Context: First mug case mold.., Coffee Mug Slip Casting..

Thursday 9th January 2025

Which common American/Canadian feldspars can substitute for each other?

Feldspars melting

Feldspars are employed in glaze recipes as melters. So comparing their melt fluidities should be helpful in deciding if one can substitute for another (of course, if possible a soda predominant feldspar should be substituted for another soda spar). Feldspars don't melt alone at cone 6 (2200F) so we mixed each with 15% Ferro Frit 3195. Nepheline Syenite is obviously the champion melter here. Other similar ones can be spotted easily. In the end, degree of melt is a valid consideration in determining if one feldspar is a viable substitute for another in a recipe. Even if the feldspar you want to substitute does not melt as much a little frit can be added to the recipe to make up for the difference (e.g. 3-5%).

Context: Nepheline Syenite, Covia Nepheline Syenite, Minspar 200, Mahavir Potash Feldspar, G-200 Feldspar, Kingman Feldspar, Custer Feldspar, Feldspar, Calculating a substitute for.., Feldspar Glazes, Material Substitution

Thursday 9th January 2025

3D-printed cookie cutters used to make this tile design

3D-printed cookie cutters to make fish tiles

Only three tile shapes were needed. The fish cutters were 3D printed to both cut and stamp at the same time. Multiple slightly different sizes of the triangle and trapezoid were made to accommodate irregularities and keep joints tighter. The clay is M340 and the glazes are Amaco Celadons and Potter's Choice (for brushing). These are small and we found that a good way to paint them was to glue them down to a plaster slab with a few drops of glaze (it was easy to scrape off when the three coats had dried).

Context: Magic tile shape grows.., Video Create a cookie.., Cookie Cutting clay with..

Thursday 9th January 2025

This is crazing. This is functional ware. Is this good?

A crazing glaze on a porcelain mug

This glaze is "stretched" on the clay so it cracks. When the lines are close together like this it is more serious. If the effect is intended, it is called "crackle" (but no one should intend this on functional ware). Potters, hobbyists and artists invariably bump into this issue whether using commercial glazes or making their own.

"Art language" solutions don't work, at least some technical words are needed to understand it. Crazing is a mismatch in the thermal expansions of glaze and body. Most ceramics expand slightly on heating and contract on cooling. The amount of change is very small, but ceramics are brittle and glazes are rigidly attached. If they are stretched on the ware cracks will occur to relieve the stress (usually during cooling in the firing but sometimes much later). All glaze and body manufacturers advise against crazing on functional ware.

Context: Where do I start.., Two matte mechanisms One.., Two ChatBots square off.., Bacterial survival studies done.., Glaze Chemistry, Glaze Crazing, Glaze Crazing

Thursday 9th January 2025

Melt fluidity is not evident on typical glaze tests

Measuring melt fluidity of a matte glaze

We wanted to compare the melt fluidity of G2934Y (left) to G2934 (right). To do that we prepared GBMF test balls (see below). The forming and drying process leave a flat spot so the gumball-sized balls are easy to place on a porcelain tile. During firing they flatten out. The degree to which they do acts as a measure of the flow (when compared with another). Many characteristics that one would not observe on glaze tiles reveal themselves in this test. In this case, we needed to know if the melt flow was at least as good (and this proves it is better). Reactive glaze tend to be the norm in recent years, their primary characteristic is being runny (having high melt fluidity). Their fired character...

Context: Preparing balls for a.., Forming a glaze into.., Melt Fluidity

Tuesday 31st December 2024

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Plainsman Clays, 671 Industrial Ave, Medicine Hat, Alberta T1A 3L5
Phone: 403-527-8535    FAX: 403-527-7508