The grogs shown here are Molochite 16/30, Christie Minerals STKO 22S and F65 Silica Sand. I wedged 150g of the molochite into 2300g of pugged porcelain (Plainsman M370). This calculates to 7.5% grog (based on 22% water content of the pugged clay). This produced the texture shown. Wedging a grog (or silica sand) into a soft clay body is easy, just sprinkle it on the table and wedge the clay over it. With each push it picks up more, the process is amazingly effective at quickly producing a homogenous material. If the clay is stiff, just moisten the aggregate. Knowing that pugged clays have about 20% water it is easy to calculate a grog addition: A 5 kg slug of clay thus contains 4 kg of powder. To add 10% grog you would add 400g. To add 10% of the total it would be 4000*10/90=444g. How much did this 7.5% grog reduce the drying shrinkage of this body? About 0.5%.
Sunday 2nd August 2020
I had this done at Shapeways.com. They offer an after-print polishing service, which I did not get. The plastic one on the left (actually printed from PLA filament) weighs 5 grams. The steel one weighs 45 grams! It cost $35 to print this. The quality is like regular stainless, this is incredibly hard! Fitting it on the shaft was the first issue. The shaft measures 8mm. My drawing sets the hole at 7.9mm. On the 3D the print with PLA I got 7.8mm, but this this arrived at 7.7mm. It required a lot of work to enlarge the hole to fit. Thus, if I were to print this again, I would set the drawing at 8.2. That should either fit or only require enlarging the hole slightly (using emery cloth). The second issue was the hole and tap for the set screw. Drilling it was very hard, the first bit broke. The second made it through, but we could not tap the threads. So we will glue it to the shaft.
Context: Propeller Mixer
Thursday 30th July 2020
Written by W. C. Worcester. He had a lab equipped with clay processing and testing equipment that many would admire today! He outlines clay geology in general, then the geological history of the province of Saskatchewan in that context. He describes the technology of ceramic materials, the major clays used in industry and the equivalent materials in the province. He submits hundreds of samples with physical test data clearly describing them and their locations (using extensive maps and diagrams). His work inspired Luke Lindoe, who continued it during the 1950s to 1970s. That inspired us to develop the testing methods used at Plainsman Clays to this day.
Tuesday 28th July 2020
Plainsman Clays did 6 weeks of mining in June-July 2018 in Ravenscrag, Saskatchewan. We extracted marine sediment layers of the late Cretaceous period. The center portion of the B layer is so fine that it must have wind-transported (impossibly smooth, like a body that is pure terra sigillata)! The feldspar and silica are built-in, producing the glassiest surface I have ever seen at cone 6 (2200F). 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 is very compatible (similar thermal expansion). But with other less compatible glazes they cracked when I poured in hot coffee. This mug was the beginning of an exciting project the sieve out +325 mesh particles any make many more pieces.
Friday 24th July 2020
Nepheline Syenite is a type of feldspar. We use it in porcelain bodies. The nepheline content determines the temperature at which the body is vitreous. We use this product in preference, where possible over soda or potash feldspar. There are several reasons: It is mined and processed in Canada and is renowned around the world for it's quality. If has a very low iron content, this makes for whiter-burning bodies. It is a more powerful flux than common feldspars. It has been very consistent over many decades.
Wednesday 22nd July 2020
These tiles are a 50:50 mix of Plainsman L215 and M390. They are fired at cone 1, 2.5 &4 (columns 1,2,3). The glaze is G3806N (v1) with stains at 10% concentrations. That glaze is a fluid-melt for cone 6, but it performs nicely down to cone 1 and even lower. There is no visible crazing and the iron body is stoneware-strength. The firings were only held for 10 minutes at cone (no slow cool). These coloured glazes are also less "muddied" by the iron in the body than would be the case at cone 6. This is a really amazing result. Red-burning bodies can be difficult at cone 6 (if fired too high the red color is lost, if fired too low they are too porous). If you do not have the frit for the N version, try G3806E or G3806F.
Monday 13th July 2020
This is what you need to be independent, to create your own manufacturing company in your garage. Some of the prices are "instead of" rather than additive. There are many approaches to glazes, the more you are willing to learn the better you will be able to make your own (and save a lot). We recommend the cone 6 range using a small test kiln (like this 220v ConeArt GX119, don't scrimp on this, go for quality and the practicality of a Genesis controller). A kiln you can fire often and inexpensively is a key enabler to learning, developing techniques, products, designs, durable and decorative surfaces, solving problems. It can be fired multiple times a day. And it is big enough for mugs and similar sizes. It will get you into the habit of using some of your creativity for experimenting. It will give you the successes early on that will inspire you to press on learning. When you are ready, then get a big kiln and hit-the-ground-running. This potter's wheel is the best available and will last a lifetime, these often appreciate in value over time. And, build yourself a good plaster table. You will use it constantly. Not shown here is a propeller mixer, also an important tool. And you will need a sink equipped with a sink trap (Gleco Trap).
Monday 6th July 2020
The shelf on the right in the traditional kaolin:silica kiln wash. Flaking constantly. Sticking on the feet of ware. A real aggravation. The one on the left is L4001, it is perfectly even. Yet thin. Much more refractory so it has not hardened or become brittle. Or cracked. And it paints on beautifully. The secret? Zircon. Zircopax, to be precise. Zircopax is among the most refractory materials in ceramics. We mixed it with some calcined, rather than raw kaolin. That greatly reduces drying and firing shrinkage and helps densify and stabilize the coverage (by its flat particle shape). Laguna gum solution was added to harden the dry layer and slow down the drying (their gum solution has a higher percentage of CMC than achievable using common mixing methods). Click the link below to get the recipe.
Monday 29th June 2020
This bowl was dipped in a non-gummed clear dipping glaze. Such glazes are optimized for fast drying and even coverage. However their bond with the bisque is fragile. The blue over-glaze was applied thickly on the rim (so it would run downward during firing). But during drying, it shrunk and pulled the base coat away at the rim (likely forming many tiny cracks at the interface between the clear and the bisque. That initiated the cascade of crawling. When gummed dipping glazes are going to be painted over, a base-coat dipping glaze should be used. What is that? It is simply a regular fast-dry dipping glaze with some CMC gum added (perhaps half the amount as what would be used for painting). There is a cost to this: Longer drying times after dipping and less even coverage. And gum destroys the ability to gel the glaze and make the slurry thixotropic.
Monday 22nd June 2020
G2934 is a popular matte for cone 6 (far left). The mechanism of the matteness is high MgO content (it produces a more pleasant surface that cutlery marks and stains less than other mechanisms such as crystallization or insufficient melting). But what if it is too matte for you? This recipe requires accurate firings, did your kiln really go to cone 6? Proven by a firing cone? If it did, then we need plan B: Add some glossy to shine it up a bit. I fired these ten-gram GBMF test balls of glaze to cone 6 on porcelain tiles, they melted down into nice buttons that display the surface well. Top row proceeding right: 10%, 20%, 30%, 40% G2926B added (100% far right). Bottom: G2916F in the same proportions. The effects are similar but the top one produces a more pebbly surface.
Thursday 18th June 2020
Find thousands more like the following: Use the search field at the top of the page at the Digitalfire Reference Library.