Is Found-clay ok for a poured J-tube??

Do i have to use store-bought fire-clay when pouring a J-tube burn-core, or can i use my left-over cob clay i dug myself in the pour mix with perilite and furnace cement??

Probably not, regarding the use of found clay. Most clays will not be able to take the temperatures that are likely. Cracking will almost always occur. I've done some pottery. A huge amount of experimentation is required in order to discover the properties of a given resource. It's not worth it unless many units are produced.

Thanks Dale,
Sorry about the two part question.
So when you said probably not, did you mean no, i probably don't have to use store-bought fire-clay, or no, i probably shouldn't use my left over, dug - myself, cob clay??

I came back and edited while you were typing. Your topic title was different than the one below. It all makes sense now.