Willie,

The sours tins work fine, and a small hole is all you need - a 4dwt or 6dwt nail makes a large enough hole.

It doesn't matter if you burn the gasses or not, but it's very stinky to not burn them, LoL! It has zero effect on the finished product either way. When we make charcoal for blacksmithing, we port all the gasses into the flames under the retort to add their fuel value to the process, but that's insignificant for making small amounts of chared cloth - you can't tell the difference. Anway, you don't really have much choice when doing this in an open campfire or in a fireplace - they are going to ignite.

It takes mere moments to char this small amount of cloth - just jump and and make some. Heck - it depends on how how and large your heat source is. Might take 30 seconds on a big bed of hardwood coals or 5 minutes in the cool flames of a poorly burning fire of damp wood. If you cool off the tin and find brown char inside, close it back up and toss it back in - no harm done. We're talking deep, deep black here. As long as you don't melt the tin (it has happened with bellows assist), the char won't be harmed by staying in longer than it needs to be.

Don't do it indoors unless in a fireplace with a draft going - your wife will justifiably get upset with you otherwise.

Have fun!

Tom