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I have some old Clay drainpipes that are about 3/4" thick. I was thinking of lining one piece that is 6"dia x 11" tall with fibre paper, filling it with scrap, and firing it. I'm thinking a 300dph to 1100..hold for 20 , AFAP to 1500 hold for 1 hour, cool to 900 then hold for many hours with a slow cooldown to room temp. Any ideas how m,any days this will take my Kiln out of commission? Thanks

Just looking through Graham Stones book...this may require more time than I want to give it...If I'm reading right its 3-4 days.

Will you be firing vertically or horizontally? If you fill it to 11" - that is a heck of large casting. Even laying down and damming the ends would be 6" thick. I don't have my copy of Stone right near me but the bigger killer is the slow drop in temperature which amounts to something like 0.5 degree/F per hour. It isn't uncommon for really thick castings (which this is) to spend upwards of a month in the kiln.

I've done this with stainless steel pipe and 1/4 inch fiber paper, and it works well--I just use a schedule for the full thickness of the entire piece, pipe and all. But for that much mass (7.5 inches), you're not talking 3-4 days, it's more like 24 days. As Jeff mentions, you'll do a half-degree per hour to 800F, which is pretty difficult for the average fusing kiln (if I can get my Skutt down to fluctuations of +/- 5 degrees, I'm happy).

One thing to note: The glass will cook down quite a bit, as much as half the length of the pipe, depending on the glass you're using. And I've sometimes had pipe leak a bit, so I set them in a margarine tub or similar container with about a half-inch of plaster refractory mix in the bottom, then let it set. It seals up the bottom so nothing leaks, and it also provides a more stable base for some of the thinner pipes.

One other option, if you can support it, is to cut that pipe into 4 inch slices and fire...