A very old technique used to teach breath control is to stand in front of a suitably mounted candle and direct your embouchure jet at it to ‘blow the flame down’ to a blue flame and hold it there. You can approach the candle closer or retreat to get an idea of the steepness of the angle of your jet of air. This improves steadiness of breath and focus.
Now, get yer flute and start a long tone. I start on low D, but any first octave note will do. Make sure your candle is securely mounted, so you don’t burn your house down by knocking it over with your left elbow as you attempt ever steeper blowing angles. This should give you a good way to know exactly where your air jet is going, and how to control it.
I’ve found this to help me with getting the ‘hard,dark tone’.
Bob
Great idea. I’ll never have to trim my nose hairs again 
Actually it reminds me of a contraption I saw at my local flute store used to teach students how to blow correctly.
Oh. I thought this might be a meta-thread. I mean, you know.
Carry on.
(Chiff & Fipple assumes no responsibility for fire-related mishaps ensuing from the above Original Post, including scorched or flaming flutewoods, scorched* lips or fingers from overheated metal flutes, attire or hair conflagrations, or the smelly aroma of said attire or hair conflagrations. Or anything else that yer mods can think of, such as but not limited to domiciliary holocausts or nearby pet mishaps. This includes crapping themselves out of alarm.)
- NOTE: “scorching” relative to the human body shall include results varying from vague discomfort to searing agony, redness, swelling, blisters, branding, or charred flesh whether intact or falling off in chunks.