Poisson Du Jour
Member
Or they might have been incorrectly referring to the need to make a black and white mask for high-quality results.
This is the single frame of film that is supplied with each and every one of my Ilfochrome prints; along one edge it has what looks like foil Christmas wrap sticky tape (often in wild patterns, including one somewhere with Spongebob Squarepants!). For years we referred to these easily-lost (and extra charge) things as "internegs", even though DW has pointed out their correct term: "BW mask".