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When the cone does this I need to adjust the program

This is a cone 04. It is bent too much, the kiln has over-fired a little (cone 03 was also bent somewhat). The built-in firing schedule goes to 1945, that would be much more over-fired than this was (and the built-in ones do not soak, drop-and-soak or slow cool). It only takes a minute to edit the program I made, all I have done is drop the step-three temperature to 1930 (it was 1935). I adjust my schedule fire-up-to temperature as needed, I cannot imagine not doing this.

Friday 10th May 2019

Soda fired porcelain vessel by Heather Lepp

This is a small cup-sized object made from Plainsman P600 (simply composed of Tile #6 kaolin, nepheline syenite and quartz). It is valued as a product-of-the-process piece, consigned to the "kiln God" as unglazed. It exhibits carbon-trap, soda glaze deposition and flashing. The soda-vapour atmosphere of the kiln glazed one side of the vessel early enough in the firing to trap carbon under a crystal-clear glass. Often such glazes are crazed, but this one likely is not because the body contains 25% quartz, giving it a high thermal expansion. The other side of the piece exhibits tones of red, brown and yellow on the bare, vitreous porcelain surface - this is characteristic of "flashing".

Friday 10th May 2019

Incredible Titanium Dioxide in a calcium matte

The glaze is G1214Z cone 6 base calcium matte. 5% titanium dioxide has been added. This Plainsman M390 tile was fired at cone 6 using the PLC6DS firing schedule. Titanium can create reactive glazes, like rutile, even with matte surfaces (provided the glaze has good melt fluidity). Calcium mattes host crystallization and work particularly well. Because titanium dioxide does not contain iron oxide lighter colors and better blues are possible than with rutile. Like rutile, the effects are dependent on the cooling rate of the firing, faster cools produce less reactivity.

Wednesday 8th May 2019

M390 mug by Sarah Pike

Wowzers! These are actually hand-made, not thrown on the potter's wheel. You can see the vertical join by the handle as it rotates. Her's is a simple concept: A red clay (M390) with a thin application of partially opacified matte glaze. She flaunts a bare red clay base, polishing it. You can find her easily on Instagram and google.

Wednesday 1st May 2019

How to give children a good experience in working with clay

Teachers who have never worked with clay face a formidable challenge with this. This read-in-three-minutes page is a complete beginners crash course in what you need to know. It explains what clay is, the advantages of working at lower temperatures, how to plan and inspire the children before starting, how to join and dry pieces, what is glaze and how to use it and how to fire the ware. The page explains things with an objective that the reader understand the basic whats, hows and whys of ceramics and pottery.

Tuesday 23rd April 2019

Low fire ware cracking during firing. Why?

Most low-fire bodies contain talc. It is added for the express purpose of increasing thermal expansion. The natural quartz present does the same. These are good for glaze fit but bad for ware like this. You could fiddle with the clay recipe or change bodies, but better to change the firing schedule. While stoneware dunting happens between 950-1150F on the way down, this could be happening anywhere. A simple fix is to slow down the entire cooling cycle. Learn to program your kiln. Use a conservative cooling rate of about 200F/hr (even slower between 950 to 1150). No electronic controller? Learn a switch-setting-schedule to approximate this down-ramp (buy a pyrometer if needed).

Wednesday 17th April 2019

Wanna throw porcelain plates with thick bottoms and thin rims?

Then they may need a week to dry! This plate had a one-inch-thick base (while the rim is a quarter of that). During the first few hours a thin rim like this will dry quickly, leaving the base far behind. But as soon as it would support the weight of a cover-cloth I put it into a garbage bag and sealed and left it for several days. Even after that it did not detach easily, even though the bat had been dry. The base was still quite soft but the rim was stiff enough to enable turning it over and trimming it (I endeavoured to create a cross section of even thickness). Then I dried it under layers of cloth for several more days. It took at least a week. Had I allowed the rim to dry out during the first few hours it would likely have cracked later on.

Tuesday 9th April 2019

GA6A Alberta Slip base using Frit 3124, 3249 and 3195 on dark body

The body is dark brown burning Plainsman M390 (cone 6). The amber colored glaze is 80% Alberta Slip (raw:calcine mix) with 20% of each frit. The white engobe on the inside of two of the mugs is L3954A (those mugs are glazed inside using transparent G2926B). The Alberta Slip amber gloss glaze produces an ultra-gloss surface of high quality on mugs 2 and 3 (Frit 3249 and 3195). On the outside we see it this glaze on the white slip until midway down, then on the bare red clay. The amber glaze on the first mug (with Frit 3124) has a pebbly surface. These are fired using a drop-and-soak firing schedule. Some caution is required with the 3249 version, it has low thermal expansion (that is good on bodies that normally craze glazes, but risks shivering on ones that do not).

Monday 8th April 2019

Buff M340 stoneware mug with natural slip glazes

Inside is GR6-A (Ravenscrag Slip with 20% Ferro Frit 3134). Outside GA6-B (Alberta Slip with 20% Ferro Frit 3195). Cone 6 drop-and-hold PLC6DS firing schedule. By Tony Hansen.

Wednesday 3rd April 2019

The matteness this glaze develops is dependant on the cooling rate

This is the G2934Y matte cone 6 recipe with a red stain (Mason 6021). The one on the left was fired using the C6DHSC slow-cool schedule. The one on the right was fired using the drop-and-soak PLC6DS schedule. The only difference in the two schedules is what happens after 2100F on the way down (the slow-cool drops at 150F/hr and the other free-falls). For this glaze, the fast cool is much better, producing a silky pleasant surface rather than a dry matte.

Wednesday 20th March 2019

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