My companion had a very bad ulcerated leg, we believe the cauce was from a fall that damaged his ankle, resulting in a plate and several screws years ago. It happened so fast at a time when he very busy having a large barn being constructed. His calf swelled to 2-3 times normal size in a day, and the skin became open and raw, about the size of a tennis ball. We couldn't get in to see our naturopath until the next day, so we found info on the internet about charcoal/flax poultice.
I was covering a large area, so I took 16'' x12" piece of clean cotton sheet, mixed 1/3 cup food grade activated charcoal with 1/2 cup ground flax seed and enough water for paste that you can spread on the cotton cloth. I would take that and wrap it around his calf. Then wrap saran wrap around that, and then wrap an ace bandage around that and pin it on for the night, 8 hours. You don't want it exposed to air, or it dries out. It takes the pain away in about 20 min. You can do it 3 times daily, but leave time to air out. And Keep the area Very clean, spray peroxide often.
We did this daily for 5-6 months. At first it drained liquid out, a LOT of liquid out. After about 4 months he showed his Dr. They panicked, did a lot of tests, nuclear bone scan and others, sent him to specialist. That Dr. came in looked at the calf, felt the leg, went back out checked tests, came back in, felt the leg for 10 min. checking for temp. We told him what we we're doing, he said, "did a lot of stuff drain out?" I said, "oh ya", he said the leg has no infection or problem he could find. After a total of 5 months we stopped the wraps, and the skin started peeling off, layer after layer... And every so often it gets to acting up, and he'll do another poultice. For the most part he only had poultice on at night.