I would do it with a light charge of Bullseye powder with a shot of old-time photographers' Flash Powder over top of it. That would work. You couldn't use Blank Fire powder because it builds huge pressures with ANYTHING ahead of it.
The Flash Powder is still being made (in New York) although about 99% of it goes to theatre groups and the film industry.
It is basically FFFg with a whole lot of Magnesium powder. The BP provides the heat and the Magnesium burns very fast, giving you a monster flash.
We had a theatrical group travelling around years ago, came to Brandon and put on a Biblical play for a solid week, 18 or 19 performances. About Day Three they ran out of Flash Powder for the big scene of the Crucifixion, so their Effects guy came to the Photography department at the U to see if we had any or could make some.
We put together a mixture of BP and Magnesium powder and he tried that. Came back the next day, said it needed a lot more "snap". So we upped the proportion of BP and it worked better but still not enough "snap" for the guy. He wanted something that would go "BANG!!" AND make a big flash and a cloud of smoke. So we gave him "snap", allright, dried out some Picric Acid (used as a stain in some very old photographic processes) and when it was dry, added that, as a powder. I forget what the exact proportions were, but the Black Powder base had a distinct Yellow cast to it. It was definitely NOT something to treat with the normal insouciance one finds in theatrical companies.
He had "snap" allright, but they were waiting for their shipment of The Real Thing, which finally got there late on Day Six, at which time he still had half of what we had made. So he used up ALL that we made, all in one flash-pot, just to get rid of it. We had told him and told him that it shouldn't be played with, but he didn't listen.
Came the end of the Crucifixion scene, Christ forgives the people who are killing him, then announces that, "It is ended...." and dies. So the Effects guy sets off this entire pot of home-made Flash Powder/Lyddite, there is a helluvva BANG!!!, a huge flash, a column of flame about 8 feet high and the Cross is propelled straight FORWARD......
........ and the front row of the audience very nearly had Christ AND the Cross in their laps!
Val Balfour, the star of the thing, held onto the Cross as if his life depended on it (it did). The Cross now was leaning FORWARD rather than backward because the Rigger had done things the easy way and put too long a backstay onto the Cross. Two Roman Soldiers thought very fast and pushed the Cross back until it was lying against its stops and main-shaft support once more and Christ could go back to being dead until it was time to take him down.
In all, it was MOST instructive and VERY impressive!
For some strange reason, he never asked us to make Flash Powder for him again!
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