In the 1980’s fine art photography went through a wrenching period. The numerous excellent fiber-based enlarging papers manufactured by several companies were suddenly facing a huge threat: RC (or Resin Coated) paper. RC paper was quicker to work with, developing fully in just about a minute and was a fast way to fully process and dry prints. Plus it dried perfectly flat, not rippled or curled up like fiber based paper. It quickly became popular. So popular that it appeared possible that all the excellent fiber based enlarging papers would disappear under the onslaught of RC. In the midst of all this apparent change, Ilford introduced a new graded high quality fiber based paper named Galerie. I tried it and really liked it, about as much as the Oriental Seagull I was using at the time. So I thought: here’s a new, excellent paper coming out even in the face of the apparent RC revolution. Good news!
RC papers were quick and easy, but quality was lacking. You could get a usable image, yet it lacked the clear whites, the deep, rich blacks and the overall brilliance of a good fiber-based paper. I tried some RC papers back then, and quickly determined that RC stood for “Real Crap.” Fortunately several excellent fiber-based papers survived the RC crisis, and all seemed fine.
Years earlier, when I first got into photography, there were several fiber based variable contrast papers available and I used DuPont Varilour paper for several years. Below your enlarger’s lens you could place a #1, #2, #3, or #4 plastic filter into a filter holder to get progressively higher contrast grades from the paper. With the earlier papers you couldn’t effectively print one part of a negative with one contrast level filter and another part of it with a different one. In the 1990s variable contrast papers with exceptional quality were introduced that used speed-matched filters.
The combination of color enlarging heads that incorporated dichroic filters for color printing and modern variable contrast papers allowed the new papers (and me) flexibility not available before. Now the filter was situated between the light source and the negative, not below the lens. With this arrangement, nothing altered the optics of the lens. So you could indeed print one part of the negative at one level of contrast, then alter the filtration (without altering the optics in any way) and print another portion of the negative at a different contrast level, blending the two seamlessly.