Hi Ellen,

This is akin to a similar question discussed some time ago - whether or
not to dilute oil before applying it to shells.  Several people said
they did dilute it, using lighter fluid or some other organic solvent.
I find it is helpful to dilute glycerin, for the same reason - a less
viscous liquid penetrates more readily.  And glycerin (also called
glycerol) is very thick straight from the bottle, a lot thicker than
mineral oil or baby oil.  It flows and pours very slowly.  And, a thick,
shaggy periostracum like that on the tritons you mentioned, can be
difficult to penetrate thoroughly.  Water of course is the diluent of
choice for glycerin.  I use hot water straight from the tap, as hot as I
can get it, and mix 50:50 with the glycerin.  This solution soaks in
readily.  If I am going to reuse the same solution later, I rewarm it in
the microwave before use.  After the solution has penetrated, the water
soon evaporates, leaving glycerin alone in the periostracum.  I think
it's better to apply the solution to a dry periostracum, either by
liberally brushing on or by dipping the shell.  If the periostracum is
already saturated with water, that water has to diffuse out before the
glycerin solution can diffuse in.  I think the idea of pre-wetting the
periostracum came about from folks who use the glycerin undiluted - a
method which amounts to diluting the glycerin on the fly, so to speak.
I prefer to pre-dilute, and apply to a dry perio.

Regards.
Paul M.