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Old 09-10-2019, 01:58 AM
Sean Jones Sean Jones is offline
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Tabular Alumina

Iím having trouble saucing tabular alumina in the UK can anyone recommend a supplier.
Iím trying to improve the longevity of me pots as Iím only getting five or so melts before they crack during warmup.
These guys https://minimeltglass.co.uk/minimelt-models/ say their pots are good for 40 to 100 melts using a 2 hour warm up! How is that possible?

I make a 40# high alumina clay pot by coiling it in a bucket shaped former. Rounded at the bottom (where the crack always is), ~3/8Ē thick at the top, fired to 2200F in a wire melter with 1 1/2Ē from wire to pot wall. My warmup schedule is 56 hours going very slow through the quartz inversions which is where I think they fail.
Pot erosion isnít an issue even though Iím using cristalica as they crack long before they get eaten.
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Old 09-10-2019, 07:31 AM
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Pete VanderLaan Pete VanderLaan is offline
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I think you might do better slip casting your pots. Dyson in England has never really made alumina pots so there may be an issue with raw source in the country. I used to make mine with
3 parts tenn ball clay
3 parts 200 mesh kyanite
3 parts 325 mesh Kyanite
Sodium silicate added to keep it all in suspension

Cast in a thick plaster mold where the plaster absorbed moisture from the slurry and the interior slurry eventually was just oured out. Those pots were good for a single firing but the firing could be months. Just don't shut it off.

The fact that the pot is always breaking in the same place might tell you about the drying rate on yours. The foot is certainly giving up moisture at a differing rate than the walls. Is the foot sitting on a surface tha absorbs moisture or is it impermeable? Or are you casting them upside down?

I don't advise making your own pots. I did it at a time when materials were not available. It's not just hard to make them, they need to be sintered and most shops can't do it. As to the mini melt, they are vague about the method but if it's invested and you don't mind fairly crappy glass most of the time , I'm sure it seems great. It's just a pot in the bottom of a gloryhole. I would wager the pot is Dyson. My friend Scott uses them in Antrim and has adjusted to the things. These days they're mostly made in Indonesia.
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Old 09-11-2019, 02:20 PM
Sean Jones Sean Jones is offline
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I started making crucibles out of necessity but now Iím more driven by interest.
Iíll add more molochite I guess as itís easily available (I live next to Stoke on Trent). I think I read in the archive that larger particles (mesh size) are better for thermal shock but suffer worse chemical attack, but I canít find the reference now. 30-80 feels right.
Iíd be interested in any books people could recommend. I looked up kyanite on YouTube. Apparently blue kyanite restores your energy balance and healers cracks in your ora. She didnít say anything about thermal shock, maybe Iíll massage her and ask.
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Old 09-11-2019, 03:05 PM
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Pete VanderLaan Pete VanderLaan is offline
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Kyanite is a synthetic mullite since the natural deposits vanished decades ago. It would be approx 76% alumina 24% silica. Molochite if I recall is a combo of actual glass and synthetic mullite ( kyanite) in a ratio about 55/45 mullite to glass, so you are getting about 1/2 the mullite which is about 75% alumina.

I would not want glass in my pot mix ever. I would consider China clay which is available where you are to make the mix more plastic but it is fine grained and therefore somewhat problematic on thermal shock.

I'm simply unaware of any literature on crucible makeup beyon the one I already gave you. So much of the effectiveness of this type ceramic is in the firing of the pot. When I say sinter, I mean sinter and that would push you up in the 2600F and higher range. One of the reasons that making pots out of 95% alumina castables don't work is the sintering issue. Most shops can't make these temps. I advise all of my clients to go as hot as they can before adding glass but these days? Skutt Kilns seem to be the new "Glass furnace".

I think it's great that you want to make your own pots as I once did. I would say that down that path lies madness.
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