cactus cutting turning black

[floring]

I recently received a cactus with a damaged lower trunk so I decided to cut it off and start fresh. The cutting area was bright green, no brown spot of any sort, no rotten/damaged part on it.

After a day or so the cutting started to turn visibly black, starting from the exterior and working it's way towards the centre of the cut. Actually it started in less than a day. It looked like oxidation, like you would get on an apple, except it was black. It's been 5 days now and it's gotten to the point where it's almost entirely black, the entire area. It's not moist. It's not soft to the touch. It's not moldy. Actually it looks like it's developing well, except it's shiny black. The cutting is in a resonably bright spot, around 20 Celsius. I've googled it a lot, but I couldn't find anything related to this. All the hits are about rotten plants.

Any ideas? Did anyone stumble into this? Don't know if it helps, it's a Stenocereus Marginatus, about 5-7 cm in diameter.

[Rod Smith]

If it's not going soft, leave it for a couple of weeks, then put it in some free draining gravel until it roots. It could take several months.

[floring]

Yesterday I noticed some moldy patches around the inner ring so I had to cut off another slice. Luckily it#s quite a big specimen and I'm not too worried of running out of slices to cut off, for now. This time, though, I used rooting powder and hopefully the anti fungal properties will help.

Not sure if the black coloration had anything to do with the subsequent mold, though. I thought it developed too fast to be anything other than oxidation, but then again, the colour was just too weird to simply shrug off.

[HP22B]

What did you use to cut this from the trunk? Whatever it was does not seem to have been sterilized very well. Hopefully the sulfur powder will help out. I would make sure you really clean whatever knife you're using with alcohol.

[floring]

It's true, I just grabbed the meanest looking knife I could find in the kitchen, and it was one that I hadn't used for millenia. I thought the cactus was going to have a woody core, but surprisingly, it was cucumber like. The second time I used a recently cleaned knife, but still no alcohol for that. I didn't think it was so important. I hope the powder does its trick.
One more thing, would it be a problem if the cactus stayed in total darkness until the cut calloused over? It crossed my mind to put it in the hot press for a month or so. It's around 23-24 Celsius and really dry air, but no light what so ever. Would it go dormant and if so, would that influence the rooting?