Quote Originally Posted by MartinP View Post
If the size is only 0,5mm on a 16x20" print I'd suggest knifing the print. Anything you do on the neg will end up a lot bigger on the print than a knifed speck.
I have not done this, but I have heard that a pin or knife-point prick on the film will optically diffract light around that area, leaving a white spot on your print for retouching. I have used a fine point red marker for LF film with some success. As someone mentioned, doing this on smaller formats means bigger areas to retouch when enlarged.