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Yeah I'm sure they were knowledgeable in their craft as any other.

If I could find a mix of matetials maybe even with some local clay as part of it last one melt I'd definitely be pleased with that.

One of the clays I found locally is incredibly hard and strong even unfired. Doesn't mean it'll survive the temperature but it's at least a starting place.

I'll probably be trying some really small crucibles as tests in the forge to see if the mix will work.

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Just a couple of broad strokes.

 

In high temp wares, clay is often your enemy. Yes. I know, it sounds stupid, but if you think of clay as a 'green strength' binder that holds together the more durable materials until they solidify at higher temperatures, you're getting my point. Try to keep the clay content as low as practicable. All they clays I used , whether Fire Clay , ball clay or Kaolin are all high Alumina clays.  In some trials I tried high iron, terracotta type clays. In low %'s , some made reasonable non-ferrous pots but most just melted at stoneware temps.

 

And as for historic practioners. It's very difficult to remove people from their materials environment and understand how they did things. Until recently, many of the 'unlikely' ingredients in old recipes were brushed off as 'magic' or 'myth'. Modern analysis has made their purpose known. An example would be straw ash. Straw ash is used in Japanese Tanren forging and in many old crucible recipes. In Europe, silver sand was used as a flux for wrought iron, but not for steel. The liquid/solid phase for steel is simply too low for coarse silica to melt. However, the silica in Straw stalks is in the 8-12 um range and will act as a flux at much lower temperatures than sand. So, the prevalent idea for many years in the West, that the Japanese used straw ash predominantly as a carbon source have been proven wrong. Likewise , straw ash ( colloidal silica in the 8-12 um range) in pots is now embraced by numerous high tech patents for carboniferous refractories as it has been found to coat graphite and prevent early oxidation.

 

Another example would be a Japanese iron patination solution that contained frankincense. Seems a bit bizarre but does make for a nice smell. Until, you talk with a biochemist working at an essential oils lab  and she inform you that Frankincense under heat breaks down to a hexane component that would act as a de-greaser.

The history of archaeo-metallurgy is replete with mysteries compounded by assumptions about our predecessor skills and knowledge, or the lack thereof.

 

FYI

Graphetised coke is a fine carbon make from petroleum products. It is identical to the coke build up you get on oil burning furnace injectors through incomplete combustion. It is far less dense than flake graphite , with an open , porous structure. It tend to burn out of pots before the body has sealed at high temp , therefore leaving a less slag resistant surface but an open fabric with much higher thermal conductivity. Very similar to the purpose of  charcoal in Japanese blade clay. My hypothesis is that controlling thermal conductivity is why both flake graphite and coke dust are found in the 'Berlin' crucible formula.

Edited by MacKINNON
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Huh very interesting indeed! Thank you so much for sharing your knowledge#! I see coke graphite for sale by the truckload basically but not just a few pounds. 

I do have some very high temperature resistant material called "Mulcoa mullite grog" 60% alumina I believe. It's actually good to know the clay is supposed to be mire if a binder for materials like this than the actual body of the crucible. That changes things for sure, good to know! I don't have graphite but powdered it is actually pretty cheap, most of the ingredients are really, I figure if I make small crucibles to test my materials won't be wasted so much if ir doesn't work. 

Another uaer on here posted crucibles made from a german kaoline mix rated to 1500°C and added fine alumina. He made several nice looking pucks and his crucibles didn't look terrible afterwards.

Have you tried the HT-100 coating on either the outside or inside? Some I've seen on Instagram showed coating theirs with a very similar coating and it making them last much longer.

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Mr. Schneider,

 

I have shown you the little I know. I have given my opinion of the use of modern coatings on crucibles. I'm sure you will develop your own recipes from research and experiments.

I am a tradesman, not a teacher.

 

Good luck with your endeavors.

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I've got the materials to try Vasily's recipe and one of the others listed , just lacking the graphite but I ordered a pound to give it a try. I'll report how it works after my furnace is built. Bricks covered in ITC 100-HT and drying overnight, tuyers molded and drying. Should be able to mirtar my bricks together and ram a coat of refractory around them. Hopefully by early next week everything will be dry and ready to go

 

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