[Nhcoll-l] Speculation on color retention and color loss in preserved herps?

[John E Simmons]

Kelly,

Color change in preserved specimens is a complex problem, as I discussed at
some length in *Fluid Preservation: A Comprehensive Reference* (2014) along
with a review the available literature on the subject. In short, changes of
color may result from chemical or physical alterations of the tissues
(usually both) and may involve color loss, acquisition, or alteration. Of
the factors that cause color change, the most significant are light UV
exposure, shrinkage, and swelling. For example, in reptiles and amphibians,
yellows and greens tend to fade quickly, but blacks and browns are more
stable. The common green-to-blue change in herps is largely (but not
exclusively) due to the leaching of xanthophories by the preservative and
the alteration of iridophores by dehydration.



Color in amphibians and reptiles involves pigments (some of which are
soluble in preservatives) and light reflection and refraction, which is
altered by the shrinkage and swelling of tissues. Color change may begin
with post-mortem specimens handling (e.g., the time interval between death
and fixation or preservation, freezing the specimen, exposure to sunlight).
Once the specimen is preserved, both visible light and ultraviolet
radiation will alter colors, as will heat. The choice of preservatives is
also a factor—colors will change in different ways if the specimen is in
formaldehyde, ethanol, or isopropanol. The colors of the specimen may be
affected by dyes from the string, tags, labels, or container, and exposure
to oxidation processes, and exposure to metals (particularly copper).



The preservation literature is full of magic recipes to preserve color,
none of which work. The only universal among the recipes is that I have
never seen an article in which the colors of the live specimen and the
post-preservation specimen were compared to the same color standard, which
means that all estimations of how well the colors were preserved were
biased guesses.



The photo that you included is interesting—that is, indeed, a spectacular
retention of colors by a snake that has been in preservative (and probably
exposed to light on view?) since 1938. Typically, that level of pattern
retention is only visible on specimens kept largely in the dark (thus
protected from visible light and UV). The snake has lost its
yellow-green-red colors (most of which are alcohol soluble pigments), but
otherwise looks good. Are there any notes in your institutional archives or
collectors field books that might tell you what technique was used to
preserve the snake? There were a lot of different chemicals in use for
preservation around that time.



Keeping the true (live) color of specimens preserved in fluid is the Holy
Grail of fluid preservation, as can be seen from the numerous publications
on the subject suggesting ways to do it. Unfortunately, all of the
published magic recipes fail the color standard test. If colors of the
specimen are important, it should be photographed before it is preserved
with a color standard reference in the photo so the colors in the image can
be corrected later.



--John


John E. Simmons
Writer and Museum Consultant
Museologica
*and*
Investigador Asociado, Departamento de Ornitologia
Museo de Historia Natural, Universidad Nacional Mayor de San Marcos, Lima


On Mon, Nov 6, 2023 at 3:04 PM Cassidy, Kelly Michela <cassidyk at wsu.edu>
wrote:

> Curious about herp preservation techniques that affect color retention and
> loss.
>
>
>
> We have a garter snake that was once used as a display and/or teaching
> specimens. It was in a straight glass tube, sealed at the ends with a black
> tarry substance. About 10 or 15 years ago, I removed the snake from its
> glass tube because the fluid and glass had become too discolored for it to
> be a suitable display specimen.  I rinsed it and transferred it to a jar in
> 70% ethanol, but I am not sure what the fluid in the original tube was. The
> snake was collected in 1938. For a specimen approaching 90 years old, its
> color pattern was unusually sharp, but it is also much more flaccid than a
> typical snake fixed in formalin and preserved in ethanol. (Picture
> attached.) Any idea what fixative or storage chemicals might have caused
> better color retention but might have been less good at preservation,
> leading to more flaccidness?
>
>
>
>
>
> On the other end of spectrum, we have a number of specimens, most from the
> mid-20th century (1950s to 1970s) that are now almost entirely bleached
> of color. These nearly white specimens came to Conner Museum as part of an
> “orphaned” collection (from Walla Walla College). Not all of the specimens
> from Walla Walla are bleached out. I am guessing there was a period when
> their fixative or storage solution contained or lacked something that
> caused unusual bleaching. We have no records from the collection about
> fixative or storage methods. What is the most likely cause of such extreme
> bleaching? Lack of buffering or chemicals used for buffering?  Storage in
> denatured ethanol?
>
>
>
>
>
> Dr. Kelly M. Cassidy, Curator, Conner Museum
>
> School of Biological Sciences
>
> Box 644236
>
> Washington State University
>
> Pullman, WA 99164-4236
>
> 509-335-3515
>
>
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