Here is what it takes to make sure P700 has minimal fired specks
We had to sample every pallet of a 1500 bag bentonite shipment. On testing each one we found dark-coloured particulates. Then we determined which pallets where the worst and did a second round of testing. Then we mixed up 5000 gram P700 test batches from three pallets, made ware and tiles, clear glazed and fired it all to cone 10R (with heavy reduction). We also prepared samples and returned them to the manufacturer for further testing in their lab. As it turned out, the dark particles were not iron-containing and we found only a few tiny specks.
Context: Bentonite, Plainsman P700
Friday 21st September 2018
Three visual glaze mechanisms make this piece unique
"
Mechanisms" are specifics about the glaze application or preparation process, the materials, the
chemistry or firing schedule that produce a specific visual effect. This is fired at cone 10R. It is made from a buff stoneware, Plainsman H550, and has L3954J black
engobe on the inside and part way down the outside. The transparent glaze on the inside gives the black a deep vibrant effect. The outside glaze is
G2571A with 3.5% rutile and 10% zircopax added (the latter imparts opacity and the former produces the variegated surface). The powerful color of the black
engobe wants to get through but it is only able to do so where the glaze layer is thinner (producing the varied shades of brown with differing thicknesses of glaze that occur because of the presence of the incised design).
Context: Mechanism
Friday 21st September 2018
The matte version covers better, looks better
This is
G2934 matte (cone 6) and
G2931K glossy base recipe having the same Cerdec yellow
encapsulated stain been added (about 10%). You really need to see these side-by-side to appreciate how much richer the silky matte version looks (and feels). AMACO has popularized the bright glossy transparent look in its 'Celadon' product line (while the effect looks good on smaller areas, for cover glazing it appears 'washed out'). An additional factor to consider is that
encapsulated stains begin to decompose around cone 6, this can produce orange-peel and
blisters on glossy glazes, but with this matte base we have not seen it happen with any color. Google 'G2934 recipe' to learn more, it is being talked about everywhere, a truly amazing base.
Friday 21st September 2018
A mug cracks before your eyes because of glaze compression
A highly
vitreous, thin walled mug is glazed inside-only. The glaze has a
thermal expansion that is too low and it is under compression, pressing outward. A tap with a spoon is enough to trigger a sudden crack. It opens under the pressure. Had it been glazed on the outside also it would likely survive, but this test still indicates that it would be better to raise the expansion a little.
Context: Glaze Compression
Friday 21st September 2018
Program your firings manually, calibrate the final temperature
Here is an example of our lab firing schedule for cone 10 oxidation (which the cone-fire mode does not do correctly). We need it to actually go to cone 10, the only way to do that is verify with a cone (self supporting cones are the only accurate way). Then make a note in the record for that schedule in your account at
insight-live.com.
Context: Controller, Cones, Firing Schedule
Thursday 30th August 2018
Polar Ice at cone 10 reduction. Stunning!
The Polar Ice data sheet has been changed. In the past we have been hesitant about firing it over cone 6. This is because it is just so
vitreous and
translucent that firing it higher seemed to be asking for trouble (like warping,
blistering). But at cone 10R it is still resistant to warping. And fires this beautiful blue-white. The
translucency, amazingly, is about the same: Incredible! This is among the most incredible pieces we have ever made in the studio here, it is hard to believe it is possible produce this kind of quality in a pottery studio.
Context: Plainsman Polar Ice cone 6 translucent porcelain
Tuesday 28th August 2018
Stunning black silky matte glaze at cone 6
This contains 6% Mason 6666 gunmetal black stain. The base recipe,
G2934, is an excellent balanced-chemistry host for a wide range of stains to produce equally stunning reds, yellows, oranges, etc. The
fritted version of the recipe,
G2934Y, provides an even better host. This glaze is affected by the clay it is on. The body on the right is highly
vitreous, this has produced a finer texture that glistens in the light. The body on the left is a whiteware having 1%
porosity (Plainsman M370). Firing schedule is also a factor, slower cooling will dull the color more. We use the
PLC6DS firing schedule.
Context: G2934Y - Cone 6 Magnesia Matte Low LOI Version, G2934 - Matte Glaze Base for Cone 6
Monday 13th August 2018
DO NOT leave outsides of functional ware unglazed
This mug is made from the strongest porcelain I have, it is so
vitreous that the bare fired surface does not even coffee-stain. So I glazed it only on the inside. That created a time-bomb waiting for hot coffee! Three others did exactly the same. Four other mugs glazed on the outside were fine. Why?
Glaze compression (the inside glaze is pushing outward) is important to avoid
crazing. But, when suddenly heated it pushes harder. Outside surface imperfections, even microscopic in size, provide crack-initiation-points to relieve the stress (the solution is an inside glaze with carefully tuned
thermal expansion or an outside glaze to counter the forces and fill in all the imperfections).
Context: Glaze Compression
Monday 6th August 2018
Mother Nature's Porcelain - From a Cretaceous Dust Storm!
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 terrasig)! The feldspar and silica are built-in, producing the glassiest surface I have ever seen (despite this, pieces are not warping in the firings at cone 6). I have not glazed the outside of this mug for demo purposes (a practice sure to fail in a crack when hot coffee is poured in).
Context: B Clay, Clay and dinosaur country in southern Saskatchewan, Vitrification
Monday 6th August 2018
Humbled by Clive Tucker
Clive Tucker and me (Tony Hansen) had a throw-off today. I got beat. I have never had to face a thrower as capable as this! He made the higher mug (on the right, we had 520 grams of clay each). It is a privilege to have, not just talented and artistic customers like this, but also technically capable ones like him. The real winner is the M370 clay we used. Even though it was too soft, neither of us had issues with twisting, it wanted to compete as much as we did.
Context: Plainsman M370, CliveTuckerCeramics.ca
Saturday 4th August 2018