black metal vocal technique.....

That being said, keep in mind that most of the most painful screeching is done by guys who hardly ever play live, so it's probably a one day out of a year thing for them anyways.
I'm guessing the best way to find answers to this is to look around for Diamanda Galas interviews, as she's probably more likely to be able to answer this than any number of teenage black metallers.

Out of curiosity, which particular style are you going for? There's obviously quite a few different approaches going around, from the Attila ca Di Mysteriis style, to Dani Filth cheesescreech, to the Burzum/Countess hilarious "anguish"-screams to the Donald Duck-style Kristallnacht vocals, to Popeye-style Immortal vocals etc.. Not to mention the more subdued approaches of the likes of Dimmu Borgir.

I talked about this with a voice teacher once in terms of the 'soul scream', how guys like Stevie Wonder, Sly Stone, J.B. etc. can get that super-high, rough scream whereas others (like me) just cannot make their voice do that. He was saying how certain ranges (maybe tenors/high baritones?) can do it more easily, while others (low baritones probably) aren't built for it.

I also remember an old interview with Dan Swano where he said he's not going to do that kind of singing live any more because it fucks him up, whereas the guy who replaced him in Edge of Sanity can do it right.

As for the screech -- again, effects can help out -- when Blixa from E. Neubauten makes a similar noise he's actually vocalizing at a low volume with a lot of processing.

that's for poseurs.

i know from experience (a misspent youth heavily influenced by "under the sign of the black mark" and "from enslavement to obliteration") that you basically have to experiment until you find a way to do it that doesn't destroy your throat; i never found a way to do the high-pitched shrieking that didn't make my throat hurt, but i did accidentally figure out how to do overtone singing.

when i hear varg vikernes sing i just picture him drinking peppermint tea with honey for a week afterward.