This may work for enlargers with Condensers. But Diffusion enlargers, popular for their ability to make dust disappear, also make this roughed up base disappear.
Originally Posted by Toffle
I have used a pin to rough up the base of my 4x5 negatives so it vanishes under the microscope. The result I get is a halo on the print. From a distance, the spot is gone. But on closer inspection it is easily apparent.
When I spot out with opaque, the printed result is very white and MUST be spotted. However the resulting spotting job is very successful.