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Andy,

It may have been me that mentioned this to you (!)...  but I think I was
talking about ethanol (still has the -ol ending, though).


Most dissected parts that workers dissect and place in a microvial under
the pinned specimen are in gylcerol/glycerin. I have never seen any fading
of specimens in this chemical medium (I have some at hand that were made
in the 1960s and still look fine).

The problem of fading/bleaching of specimens stored in alcoholic fluids as
far as I have been able to determine is not the alcohol, but the chemical
used in denaturing it. For example, if pure ethanol is used, there is no
bleaching. I have seen type specimens of flies over 100 years old in their
original spirit preservative still as pristine in their black and brown
color* as freshly collected ones. I would assume (but cannot know for sure
without experimentation) that the chemistry is the same for all alcohols
(those with an OH in their makeup), so it should theoretically work for
glycol and glycerol as well (at least the 50+ year evidence seems to be so
for the dissected specimens done in the 1960s that are in glycerol).

I seem to remember this being discussed on the NHCOLL-list at one time. (?)

*NB: It is the brown/black melanin in the cuticle that fades with the
denaturing chemical. Pigments giving other colors will fade over time in
any medium (except photographic ones). Adding distilled water to an
ethanol solution should not cause fading either as melanin is not
water-soluble.

-Neal




On Stardate 11/11/14 7:13 AM, "Andy Deans" <[log in to unmask]> wrote:

>Hi all,
>Can anyone recommend articles that describe research on the long term
>effectiveness of specimens stored in propylene glycol or glycerol
>(glycerin)? All I can find are articles that explore the quality of DNA
>in specimens stored in these preservatives. What I really want to know
>is: how are specimens affected over the long term, like 50 or 100 years?
>Do they fade or rot? Are they affected in other ways? And are there any
>taxon-specific effects (e.g., are spiders okay in glycerol over the long
>term)?
>
>Someone mentioned to me that they have seen specimens (Diptera maybe)
>that were stored in glycerol for many decades, maybe over a century, and
>they seem to be in great shape.
>
>Thanks for any info! See you in a few days,
>Andy


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