In addition to fresh water shells, land snails also
frequently have the colors and pattern in the periostracum, but not all of
them, and sometimes this can be difficult to determine by looking at the
shell.  Some land snails have a fairly thick periostracum which obscures any
pattern or color of the shell itself.  Such shells are usually bleached to
remove the periostracum, and generally such shells, once bleached, do have
some color. Other land shells have a thin, translucent periostracum, which
allows the shell colors and patterns to show through. Many collectors like
to remove this kind of periostracum, since it may give a yellowish cast to
the shell, and mute the colors. However, this is where collectors may run
into trouble. In some land snails, all the color and pattern are in the
periostracum, rather than the shell. Others have colors and markings in both
shell and periostracum, and the appearance of a fresh specimen is actually
an overlay of the periostracal pattern over the shell pattern. Bleaching
shells of this kind can provide some interesting (or disastrous, depending
on your point of view) results. The beautiful, large, green-banded
Helicostyla portei, if exposed to bleach, will come out as white as a
snowball. It's color and pattern are entirely in the periostracum.
Incidostoma confusum, a large operculate land snail from South America,
appears bicolored in natural condition, the upper half of the shell light
brown, the lower half dark brown. After bleaching, it is pure white, except
for a pink apex. In some Chrysalis species the spiral, or transverse
markings are on the shell, but the axial markings are a periostracal
overlay. Bleach it and you have spiral pattern only. Helicostyla grandis in
life appears light greenish brown with multiple bands and irregular
splotches of dark chocolate brown. After bleaching, it is uniformly dark
brown, fading to white toward the apex. The light brown color seen in life
is periostracum, and the dark bands and "markings" are actually uncolored,
transparent areas of periostracum, where the underlying dark shell color
shows through. Placostylus hargravesi, a beautiful, elongate, olive-colored
shell with intricate darker markings also bleaches pure white - except for
the interior columellar area, where the periostracum was overglazed by the
snail!  Helicostyla pan is another interesting one, a very attractive shell,
both before and after bleaching. Before bleaching it has multiple spiral
bands ranging from deep chocolate brown through lighter brown, tan, and
white. After bleaching, the banding is gone. The lower half of the body
whorl is deep chocolate brown, which extends up along the suture line. The
upper half of the body whorl is tan, fading to white near the brown suture.
The shell also has a nice gloss, another feature which is hidden by the
periostracum.  So, while many land shells can be bleached safely, if you
aren't sure, try your least desirable specimen first, and avoid unhappy
surprises.