For the photographic darkroom unsharp masking, a large-format glass plate negative is contact-copied onto a low-contrast film or plate to create a positive image; which is made with the copy material in contact with the back of the original, rather than emulsion-to-emulsion, so it is blurred.
For the photographic darkroom process, a large-format glass plate negative is contact-copied onto a low-contrast film or plate to create a positive image. However, the positive copy is made with the copy material in contact with the back of the original, rather than emulsion-to-emulsion, so it is blurred. 
