Once again the technical equivalent is obvious:
it consists
in the absolute continuum from brightest light to darkest shadow.
Here, too,
we see in operation the law that new advances are prefigured in older
techniques, for the earlier art of portrait painting, before its disappearance,
had produced the strange flower of the mezzotint. The mezzotint process
was of course a technique of reproduction, which was only later combined
with the new photographic reproduction.
