Place your batteries in the battery compartment of your electric flash pot. Make sure the switch is set to "Off."
Place a small amount of white flash powder in your flash pot (2 to 3 tablespoons). How much flash powder you'll need will depend on how bright you want your flash to be. The flash powder creates a small explosion, however, so be very careful not to use too much.
Conceal your flash pot within your flameproof curtain. If you cannot find a flameproof curtain, you can add flame retardant to a normal curtain. You will want to create a prop that will be very near the prop camera used on stage. Old bellows cameras from the early 20th century were shrouded in a black curtain. If you are attempting to replicate that kind of camera flash, then your work is easier. If you are replicating a camera flash of a newer or handheld camera, you will have to create a stage setup that will allow you to hide your flash pot in something easily accessible by your actor or by a stagehand.
Activate the switch on your flash pot when you are ready to create the flash.
Conceal a small handheld strobe light within the camera or flash apparatus.
Plug the strobe light into an extension cord.
Plug the extension cord into a power strip. Make sure the power strip is set to "Off," and plug it into the wall.
Set the strobe light to create a very slow flash.
Press the "On" switch on the power strip (or have a stagehand do it) when you are ready to create your flash. Turn the power off immediately after the flash has been triggered.