In Judith and Richard Carter's book on Fink's graphic works, a print titled "Coco's Blouse" is listed as having been done in 1964. However, this impression is dated 1969, and unlike the ink listed in the 1964 description, this impression doesn't just use black. In this impression there are areas of another, paler ink overlaying the black which gives it a kind of solarized effect, as in photography.
Carter later lists two other impressions, not illustrated, that are simply titled "Experimental prints" (192 and 193) and are described as having a "solarized effect". We are presuming that Fink was experimenting with this unknown technique when he printed this impression. An interesting mystery.
Also mentioned in Carter's description of "Coco's Blouse" is this notation: "In the opinion of many, including the artist, this print is considered one of Fink's best works."