Graphite and other refractory materials can be found at the Graphite Store. A large variety of components, crucibles, tubes, etc., fabricated from SIALON, zirconia, alumina, or graphite, can be found. Graphite items are surprisingly inexpensive. Great for that dungeon or backyard foundry.
Lamentations on Chemistry
Editorials of a Scientist Political
Lamentations on Chemistry 
When dealing with hot graphite in air beware carbon monoxide. It’s magic stuff – molten glass does not wet it. Excitement is a quarter cup of fused goodness zooming through a quarter inch of densified graphite, two inches of firebrick, a benchtop, two shelves, and making a pretty good run at the cement floor. No matter – we had more graphite crucibles.
So, what went through the all of the material???
Devil Solvent. We’re occasionally trying to chemically grow diamond from molten salt synthesis at ambient pressure, sort of a condensed phase CVD. Also does a job on alumina, fused silica, zirconia, porcelain, mullite, carborundum… copper, nickel, nichrome, silver… Diamond dust is unaffected, graphite simply disappears. Devil Solvent is not unfriendly, it’s just particular about relationships.
The chemistry seems reasonable. The engineering, including control, is something of a challenge. Homeland Severity gives us grief for one of the reactants. Idiots.
Gosh, now I’m really intrigued. Looks like you need a diamond lined crucible.
It works on paper. Finding a solvent inert to carbon radicals brought us to molten salts. Containment is (now) reasonably accommodated. We need one isolated wire in there for control feedback. No dielectric survives the environment. The clever solution is finicky.
We’d be happy with abrasive though a big plop of clear single crystal is OK. About 100 pm boron makes diamond phosphoresce red-orange for 60-90 seconds after 254 nm UV. If it is in the workup we can find it in the dark. It’s a hobby.