  We investigated the formation of KCl crystals on glass surface by phase
contrast, fluorescent, and atomic force microscopy on the micrometer scale, and
observed interesting morphological transitions as a function of the
experimental conditions. The presence of proteins in the solution from which
the salt crystals grow during the drying up leads to complex microscopic
patterns of crystals some of which are analogous to those commonly observed on
the macroscopic scale. We tested the effect of tubulin, FITC-labeled albumin
and IgG on the morphology of crystals grown either slowly or fast. A rich
variety of protein specific and concentration dependent morphologies was found
and described by a morphological diagram. We give a phenomenological
interpretation, which can explain the growth of complex patterns. Fluorescent
images prove that a protein layer covers the surface of the KCl structures. We
propose that this layer reduces the anisotropy of the effective surface tension
during growth. The tip splitting fractal regime is attributed to the decrease
of anisotropy. Other possible mechanisms, which can cause morphological
transition, are also discussed. We found elongated saw-toothed crystals induced
by proteins, especially IgG and identified their structure.
