Could you explain the timing of the entire painting procedure and the exposure for the model?
Ha ha, putting me on the spot here but I'll try to recall as much as I can.
We set our cameras to manual, set our exposure to 'bulb' and set up rear curtain sync. The windows were blacked out and the room was pretty dark. Of course you focus on the model first while the lights were up. There was a flash set up on the model which happened to be an optical slave although it could have been any flash set to trigger with your shutter release and other light, I guess it would be called a modelling light. Because of the long exposure you must use a tripod but I didn't have one with me. I borrowed a monopod for some but it is not as stable obviously.
Lights down, open your shutter and someone takes a flashlight and 'paints' patterns in the air trying not to go in front of the model. Once they are done, they leave the scene and you trigger the flash, thereby freezing the model with it and shutting your shutter.
That's about as much as I can remember, although I am sure there are members here who will be able to fill in the gaps as there are some very accomplished photographers in this forum. Next time I will try to be better prepared.
The exposure was roughly 16 secs.
Here are two shots showing the shot in colour and the set up showing the flashlight operator leaving the scene before the final flash