rosive used by
Rembrandt to bite his plate.[28] Only tentative conclusions can be drawn
from this and other prints. The etched lines in the _Landscape with a
hay barn_ ... appear to be bitten with a fairly strong acid. The lines
are relatively broad in relation to their depth, a strong-acid effect.
Furthermore, illustrations of some of Rembrandt's original plates from
this period show a similar broad line.[29] In addition, in the
photograph (figure 14) of at least one of the plates there is seen a
peculiarly ragged line which is often caused by bubbles formed on the
plate by acid action.[30] This appearance of bubbles is characteristic
only of the strong acids. Of the acid formulae suggested by Bosse in
1645, only one--a distillate of vitriol, saltpeter, and alum--appears to
be strong enough to produce the observed effects.[31] Generally
speaking, Rembrandt's later etchings show evidence of stronger acid
biting than his earlier work, which has more of the characteristics of
weak mordants.[32] Certainly, a strong acid would produce a much
speedier biting and bolder etched lines, providing him with a solid
foundation for his fine drypoint work, and enabling him to work
continuously, with a minimum of delay.

[Illustration: FIGURE 13

Detail of Rembrandt's finished print, _Landscape with a hay barn and a
flock of sheep_, lower right, showing lines of pure etching. Enlarged 10
times. (Smithsonian photo 59387.)]

[Illustration: FIGURE 14

Detail of the etched copper plate for Rembrandt's print, _Christ seated
disputing with the doctors_. After Coppier, p. 117. (Smithsonian photo
59395.)]

[Illustration: FIGURE 15

Detail of Rembrandt's finished print, _Landscape with a hay barn and a
flock of sheep_, far right, showing drypoint drawing of sheep and post.
Enlarged 10 times. (Smithsonian photo 59388.)]

Rembrandt's use of drypoint is, as Jakob Rosenberg says, "the most
important innovation in Rembrandt's mature graphic work."[33] After
etching his skeletal design on the plate, he went to work with his
drypoint needles--long, stiff, iron instruments--sharpened to a fine
point. An artist generally has several available, so that he does not
have to stop and re-sharpen in the course of his work. Rembrandt
evidently went even further and deliberately used dull needles to obtain
certain light line effects.

When the finished print is compared with the sketch of the etched lines
alone, it can be seen how vital the drypoint