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Plainsman Pottery Supply is now open for in-store shopping. We are limiting in-store shopping to 4 people at a time, and properly fitted masks are required.

Curbside Pickup orders may still be placed via email at larry@plainsmanclays.com, or over the phone by calling 780-440-4791.

Click the links to the left to get information and pricing on our products. Click the "Plainsman Data Sheets" for details information on the use and Plainsman clay bodies and glazes. The blog below is intended to help you with all manner of technical issues in ceramic hobby production, these posts come every few days, so check back often.

Technical Tips Blog

Amaco underglazes can contain very high percentages of stain

Top are V-326 and V-388 underglazes, painted on and 04 bisque fired. Although the layer is very thin the coverage is amazing and the brightness is stunning. This degree of brilliance is not possible unless the percentage of stain is very high. That explains whey these are double or triple the cost of a typical commercial glaze. The bottom mugs are clear-glazed and 05 fired, the one on the left with Amaco LG-10 and the one of the right is Spectrum 700. The latter produces better results over the underglaze and is more transparent and less yellowish on the body.

Context: Underglaze

Tuesday 18th January 2022

Iron oxide as a fining agent to debubble a low fire transparent

One glaze is transparent, the other milky because it is filled with micro bubbles.

These terra cotta clays were bisque fired at cone 04 and glaze fired to 04 using the 04DSDH schedule. The glaze is G1916Q, an expansion-adjustable cone 04 clear. That schedule alone is often enough to get transparent, defect free glazes in many situations. But not in this case. The solution was to add a fining agent. In this case we added 2% red iron oxide (to the top glaze). The particles of iron floating in the melt acted as a congregating points for bubbles, helping them to escape. And we got a bonus: a more interesting aesthetic. A 1% addition also worked, but not as well (we have settled on 2% iron and screening the glazes to 100 mesh). Screening out the larger particles slightly degraded the fining performance (so we have to accept the tiny specks). Iron does not always workin other situations. Other fining agents we have used at cone 6 do not work in this situation (e.g. 2% Zircopax, Alumina). Of course, this glaze will fire amber on a white body.

Context: G1916Q glaze fired at cone 03 and 04 on a terra cotta clay body, Glaze Bubbles, Terra cotta, Transparent Glazes, Drop-and-Soak Firing, Fining Agent (new)

Sunday 16th January 2022

Alberta Slip GA6-B base darkened with iron oxide

Glazed tiles showing darkening with increased iron additions to GA6-B

Fired to cone 6 using the C6DHSC schedule. Top: GA6-B. This recipe is 80% Alberta slip and 20% Ferro Frit 3195 (we used to use frit 3134 but have found frit 3195 works much better). Bottom: We added 1, 2, 3 and 4% iron oxide. At about 2%, the color matches the rich reddish effect you would get if you used an 80:20 Albany:3195 recipe (without an iron addition). An added benefit is that the iron acts as a fining agent to remove micro-bubbles to achieve better transparency.

Context: Albany Slip, Alberta Slip, GA6-B, Fining Agent (new)

Sunday 16th January 2022

G1916Q glaze fired at cone 03 and 04 on a terra cotta clay body

Two clear glazed terra cotta mugs

The body is Plainsman L215. Both were thinly applied and fired using the 04DSDH schedule. The glaze has 2% iron oxide added and sieved to 80 mesh, this reddens the color and acts as a fining agent to reduce micro-bubble population. The one fired to cone 03 (left) is considerably stronger, better surviving the stress of successive impacts with a hammer. However, it has minute dimples in the surface, likely because it is having to clear bubbles originating from decompositions occurring in the body below (as it fires well above bisque temperature). The mug on the right fired about 40F cooler, between cone 04 and 05, only slightly above bisque. The glaze surface is much better, almost crystal clear. Since the glaze fits well the mug has surprising strength, much better than a stoneware piece with a poorly fitted glaze that shatters with one tap of a hammer. This one survived about ten whacks before a piece broke out! A big advantage of cone 04 and cooler is that ware can be fired on stilts, meaning you can glaze the whole thing, no bare clay is exposed. Again, I can only achieve this kind of glaze surface using the above-mentioned firing schedule.

Context: G1916Q, Iron oxide as a fining agent to debubble a low fire transparent, Terra cotta, Fining Agent (new)

Sunday 16th January 2022

G1916Q transparent on terra cotta body at cone 06, 05, 03

Three clear-glaze terra cotta mugs with rich red color

The body is Plainsman L215. We used the 04DSDH firing schedule. The glaze is inexpensive to make so we have a 2 gallon bucket. It has good dipping much like a stoneware glaze so it is easy to apply quickly and evenly. For most terra cottas, body strength increases dramatically by cone 03. However the most transparent and glassy glaze surface happens at cone 06. Terra cotta bodies need to be bisque fired fairly low (e.g. cone 06) to have enough porosity to work well with dipping glazes. After cone 06 they generate increasing amounts of gases (as various particle species decompose within), for this reason the glazes can have more micro-bubble clouding or tiny dimples in the surface. This glaze has 2% iron oxide added as a fining agent to remove the bubbles. That iron also reddens the color and variegates the surface somewhat. Even though the surface character at cone 03 is not a smooth, it has a natural charm, and the color is very rich. And that piece has stoneware durability and strength.

Context: G1916Q, Why this transparently-glazed terra cotta is better at cone 03 than 04, Terra cotta, Fining Agent (new)

Sunday 16th January 2022

Making a QRCode using porcelain pixels

A QRCode made from porcelain pixels

I 3D-printed a stamper to create 9mm square pixels. Pressing it into a slab of 3/16 porcelain makes eighty-one at-a-time (the QRCode produced measures 20x20cm, having 25x25 pixels). The black porcelain has 5% Mason 6666 stain. Firing temperature was cone 6. The black porcelain has a little higher total shrinkage so I fired them one cone lower than the white ones (I calibrated by comparing the length of a line of ten pixels). The pixels dry and shrink and drop out of the stamper easily. The action of the stamper rounds the upper corners of each. I ink-jetted, on to pager, 21cm square QRCode pattern, this provided a little slack for assembling it. Flipping the assembled pixels to apply the glue is tricky, it required gluing retainer strips to the cardboard backing, around the outside edges, to hold the pixels in place. For the next one I plan to glue the pixels to a zero-fired-shrinkage clay tile, made from L4410P. A little silicon sealant on the tile and that will be suitable outdoors. What does this QRCode say? https://plainsmanclays.com.

Context: Porcelain pixel QRCode is scannable. Try it!

Monday 10th January 2022

You may know Veegum T but do you know VeeGum CER?

Attempts to use a glaze that is too thick

The glaze in this jar was 'goop', impossible to paint on because it was too viscous. And it dried way too fast. Laguna mentions adding water so I measured the specific gravity (SG): 1.7. That is super-high, it took a 125cc addition to bring it down to 1.5, but it was still thick, dried even faster and brushing it on evenly was even harder. It was not obvious what to do next. It needed a lot more water (1.3-1.35 SG is normal to support multi-layer application), adding CMC gum and enough water to do that would produce an unusable watery and sticky slurry. Veegum CER to the rescue! It is a 50:50 mix of CMC gum and Veegum T. The former slows drying and hardens, the latter gels. So it can simply be added until the painting properties are right. And, a Veegum CER solution is easier to handle than one of CMC gum. This really worked! The brushing properties are just right and it gels nicely on standing. CER is also good for highly fritted dipping glazes or others lacking in clay content (otherwise CMC might still be better).

Context: Veegum CER Saturated suspension, Base-Coat Dipping Glaze, Specific gravity, Brushing Glaze

Wednesday 5th January 2022

Improving a dipping glaze with a measured CMC addition

A pail of glaze needs CMC gum

The problem: This dipping glaze is crawling (as shown on the glazed tile). Fortunately, the slurry has settled about an inch, that provides an opportunity for an immediate fix: Remove some of the water and replace it with gum solution. I want to replace about one tenth of the water (to be between a base coat dipping and brushing glaze). The bucket calculates to 2549g of powder so I need to remove 217g of water and replace it with gum solution. One way is to use a small sponge: Wet and wring it out and then repeat touching it to the water surface and wringing it out into a container until 217g. A propeller mixer is needed to mix in the added gum solution (it won't just stir in). Of course this degree of weight-precision may seen to be overkill, but having a record of what was actually done to adjust the slurry is important to repeating it the next time it is prepared or as a base for further adjustments.

Context: CMC Gum, How to convert a dipping glaze to a brushing glaze, CMC Gum Calculator - Worksheet

Wednesday 5th January 2022

Common dipping glazes converted to jars of brushing glazes

These are cone 6 Alberta Slip recipes that have been brushed onto the outsides of these mugs (three coats). Recipes are GA6C Rutile Blue on the outside of the left mug, GA6F Alberta Slip Oatmeal on the outside of the center mug and GA6F Oatmeal over G2926B black on the outside of the right mug). One-pint jars were made using 500g of glaze powder, 75g of Laguna CMC gum solution (equivalent to 1 gram gum per 100 glaze powder) and 280g of water. Using a good mixer you can produce a silky smooth slurry of 1.6 specific gravity. However most commercial glazes do have a lower specific gravity (have more water), this does aid further in paintability but requires more coats. Amazingly, the presence of the gum also makes it unnecessary to calcine the Alberta Slip.

Context: CMC Gum, Where do I start in understanding glazes?, Brush-on commercial pottery glazes are perfect? Not quite!, Brushing Glaze, Glaze Layering

Wednesday 5th January 2022

Crawling in G2934Y zircon white glaze: There are simple fixes

A matte glazed G2934Y mug where the glaze has crawled on the upper handle join

G2934Y is a fabulous base glaze but it is not without issues. It has significant clay content in the recipe and high levels of Al2O3 in the chemistry, these make it susceptible to crawling. While it is normally fine as is, when you add certain stains to color it (especially at significant percentages) or opacify it using zircon (this has 10%), it can become more susceptible to crawling. On this mug, the glaze layer thickens at the recess of the handle join, that produces crawling during firing. Crawling can also happen on the insides of mugs, where wall and foot meet at a sharp angle. This happens, both because the glaze cracked here during drying and because the zircon stiffens the melt, making it less mobile. Adjusting the glaze recipe so it shrinks a little less on drying is an option (by trading some of the raw kaolin for calcined kaolin). But easier is to add a little CMC gum, start by letting it settle and replacing 10% of the water with gum solution.

Context: G2934Y, CMC Gum, G2934Y variations for fired hardness, COE adjustment, less crawling, etc

Tuesday 4th January 2022

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Plainsman Pottery Supply, 9517 - 41 Ave NW, EDMONTON, AB T6E 5X7
Phone: 780-440-4791, FAX: 780-490-7591, Email: larry@plainsmanclays.com