Maybe a slightly opaque word? One however we used to use constantly in book manufacturing in pre-computer days. When you print a book by offset lithography any extraneous marks which get incorporated into the film negatives have to be painted out with an opaque ink-like fluid. Anything on a negative which isn’t black will reproduce on the plate, where, when the light goes through the negative, everything black will become white and everything white black. The opaquing fluid tended to be a chestnut red liquid which the spotter would apply with a paint brush. When you looked at a flat (a bunch of negatives stripped up in imposition order) it was a rather colorful sight — black squares of film held by red tape on an orange carrier (which was called goldenrod), the whole dotted with chestnut colored splurges of opaquing fluid.

Behold a failure of opaquing:

Below the printer’s address there are two horizontal lines. These are shadows: clearly something was cut out here after the repro proof had been pulled, and was (presumably) replaced by a strip of plain white paper. When the repro was shot by the camera the lighting caught the edges of this strip and saw the resultant shadow as a line. Did we, the publisher, not check a set of blues? Looks like we didn’t — or if we did, we did it with our eyes shut! On the facing page we managed to miss another similar mess, where, presumably, the page numbers for the indexes weren’t known when the repro was pulled, and were subsequently cut in as repro corrections; then embarrassingly missed by the production department. Maybe volume two was running late and we had to rush it through to catch up with the first: can’t remember. Halliday Lithograph Company was certainly considered a good printer. — they were unfortunately one of the earlier of the northeastern book printers to exit the scene.

Perhaps we were making a silent comment on the inferiority of offset lithography to letterpress printing in a book all about the revolution in knowledge consequent upon the invention of letterpress printing from movable metal types!