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

Tue Nov 7 00:44:53 EST 2023

A common cause of color fading in liquid preservation, which
unfortunately is often not considered, is the denaturant used in
denatured alcohol.
In Germany, this is often butanone (also known as methyl ethyl ketone,
MEK), a very aggressive solvent. At least with insects, I
have noticed that the colors suffer from this.

All the best

Joachim

--  
Joachim Haendel

Center of Natural History Collections
of the Martin Luther University (ZNS)
- Entomological Collection -

Domplatz 4
D-06099 Halle (Saale)
Germany

Phone:  +49 345 - 55 26 447
Email: joachim.haendel at zns.uni-halle.de

>>> Simon Moore <couteaufin at btinternet.com> 07.11.2023, 00:05 >>>
As John said, finding a true colour preservative, rather than one that
does an OK job is indeed the Holy Grail of fluid
preservationists! Certainly, storage in the dark eliminates / reduces
UV-exposure but some chromatophores are highly vulnerable to
chemical as well as light changes. Throughout my long career, I have had
good results (but only good, not perfect) from various
techniques but unless the conservators / preparators actually record
their methods and reagents used, then this can become rather
a lost cause once again!

As an example, I am still trying to find a preservative for chlorophyll.

With all good wishes, Simon

Simon Moore MIScT, RSci, FLS, ACR
Conservator of Natural Sciences and Cutlery Historian.

www.natural-history-conservation.com

> On 6 Nov 2023, at 22:20, Cassidy, Kelly Michela <cassidyk at wsu.edu>
wrote:
>
> I think it was probably prepared by George Hudson, who was Conner
Museum director from 1938 or 1939 to 1972 (died 1973). After
he came to Conner, his focus was primarily on birds and mammals. He was
a superb taxidermist. Most of the birds and mammals, plus
a few mounted herps, were prepared by him. He collected herps when he
was in Nebraska and some herps after he came to Conner, but
I haven’t found any notes of his on herp prep. If it was Hudson who
prepped it, I don’t think he used the same techniques as for
his research specimens. They have fairly decent color (for their age),
but not as sharp as this garter snake and his research
specimens aren’t flaccid.
> Dr. Kelly M. Cassidy, Curator, Conner Museum
> School of Biological Sciences
> Box 644236
> Washington State University
> Pullman, WA 99164-4236
> 509-335-3515
> From: John E Simmons <simmons.johne at gmail.com>
> Sent: Monday, November 6, 2023 1:41 PM
> To: Cassidy, Kelly Michela <cassidyk at wsu.edu>
> Cc: nhcoll-l at mailman.yale.edu
> Subject: Re: [Nhcoll-l] Speculation on color retention and color loss
in preserved herps?
> [EXTERNAL EMAIL]
> 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 formaldthe 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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NHCOLL-L is brought to you by the Society for the Preservation of
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mission is to improve the preservation, conservation and management of
natural history collections to ensure their continuing value to
society. See http://www.spnhc.org for membership information.
Advertising on NH-COLL-L is inappropriate.
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