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

Tue Nov 7 09:34:22 EST 2023

.. and often herpetology specimens are only injected, but not tossed into fixatives or (pseudo)fixatives; might be another key factor to consider in this specific case ....

Am 07.11.2023 um 12:28 schrieb a.j.van_dam at lumc.nl<mailto:a.j.van_dam at lumc.nl>:
Dear Kelly,

The most stable organic pigments (melanins) are found in keratin. This is well demonstrated by the direct detection of melanin in dinosaur fossils. These pigments in keratin-rich tissue like (snake) skin and hairs can sustain quite a long time when preserved in ethanol. However, the other tissues of the specimen will lose their colour much faster and become pale/whitish in appearance.

Besides its flammability and high vapor pressure, another disadvantage of ethanol is that it dissolves lipids and extracts fat soluble organic piments (like carotenoids), leading to loss of tissue colour and yellowing of the fluid. Using glycerol 65% as an alternative solves these two problems. Glycerol has extreme low vapor pressure and does not dissolve lipids due to its high polarity.

With regard to the observed flaccidness, it might be possible that in this case fixation was only performed with ethanol (pseudo) fixation.

Kind regards,

Dries

Andries J. van Dam<https://www.linkedin.com/profile/preview?vpa=pub&locale=en_US> | curator-conservator

Anatomical Museum<https://www.lumc.nl/onderwijs/over-ons/anatomisch-museum/?setlanguage=English&setcountry=en> | Directorate of education | Leiden University Medical Center | Building 3 (V3-32)
P.O.Box 9600 | 2300 RC Leiden | Netherlands
Visiting address: Hippocratespad 21 | Tel: +31 (0)71 52 68356 | E-mail: A.J.van_Dam at lumc.nl<mailto:A.J.van_Dam at lumc.nl>

Scientific associate | Natural History Museum London

From: Nhcoll-l <nhcoll-l-bounces at mailman.yale.edu><mailto:nhcoll-l-bounces at mailman.yale.edu> On Behalf Of John E Simmons
Sent: maandag 6 november 2023 22:41
To: Cassidy, Kelly Michela <cassidyk at wsu.edu><mailto:cassidyk at wsu.edu>
Cc: nhcoll-l at mailman.yale.edu<mailto:nhcoll-l at mailman.yale.edu>
Subject: Re: [Nhcoll-l] Speculation on color retention and color loss in preserved herps?

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<mailto: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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Stiftung des öffentlichen Rechts;
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