Filming fire

[woods01]

For an upcoming movie there will be a shot
where a mirror frame will burst into flame.
I am not sure how to expose this shot. Since the fire starts in mid shot should I underexpose by a stop. Or should I just set the exposure for the shot based on the
unignited mirror and let it be a bit over
exposed once the fire starts? Any lighting
tips for fire?

We'll be shooting black and white but I have
not yet decided whether to use Plus-X or
Tri-X.

[Nigel]

I seem to always shoot a film that has a fire shot in it for some reason. I learned a long time ago that--"Fire can only light itself." You can never expect fire to cause the great mottled light on the subject. It won't happen.

Light for the subject. Expose for the subject. If the subject is the fire then expose for that. If the subject is the person in the mirror then expose them best. Always light the subject.

Good Luck