Hello Paul,

To address a few of your points -

Glycerin is a highly stable compound that keeps virtually indefinitely
without refrigeration.  It does deteriorate somewhat from exposure to
light (especially UV), which is why it is usually sold in dark brown
bottles.  I have seen food grade glycerin sold in clear bottles however.
 The phrase "100% pure" is never technically accurate for any purchased
compound, including the sugar and salt we sprinkle on our food.  But,
either reagent grade or food grade glycerin is essentially pure,
nortmally with no contaminants present in greater than 0.005%
concentration.  Glycerine is fairly inert chemically, but does react
with a few very strong oxidizers, in whose presence it can generate
enough heat to cause a fire.  I have used this as a classroom
demonstration many times.  Glycerin does not react with the acids you
mentioned, but it DOES react with NITRIC ACID!!! - producing that famous
substance widely used for blowing up stumps and demolishing buildings,
before the advent of "safer explosives".  It is a poor cellular
preservative, but periostracum doesn't have a cellular structure.  It is
composed of acellular fibers of conchiolin.  Glycerin does not
"preserve" periostracum in the same sense that formaldehyde preserves
proteins or cells.  It does not bind to or react chemically with the
periostracum in any way.  It simply keeps the conchiolin flexible, so it
does not tend to chip, crack or peel, as it does when it dries out.  In
a sense, it keeps the periostracum "perpetually wet".  Well, not exactly
perpetually, because glycerin does evaporate - but at a rate thousands
of times slower than water.  After some years, it may be necessary to
re-treat specimens.  The down side of treating periostracum with
glycerin is that dust and lint tend to stick to it.  A glycerin-treated
periostracum doesn't really feel "sticky" to the touch.  It's more like
it is "damp", and dust tends to stick to damp surfaces more readily than
to dry surfaces.

Regards,
Paul M.