With pinhole, you'll usually be kinda guestimating exposures anyway so, you kinda have to free yourself from worring too much about the little things.
Originally Posted by markbarendt
True, the foil is fragile. It works best if you also make some kind of shutter so that you don't actually ever touch the foil. I usually tape the foil to the inside of the lensboard and use a piece of card stock to fashion a primative shutter to the outside. You can evensandwich the foil between a couple of small pieces of corregated cardboard on the inside of the lensboard. This way the foil stands off from the lens board a little bit and survives much longer.
The cool part about using foil is that you can easily experiment with differnt size and shape pinholes.