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

Tue Nov 7 01:53:39 EST 2023

Yep, concur with Joachim that denaturants or other additives can play a significant role; cf. Plate 9 in our fluid book; US<https://www.universityproducts.com/best-practices-in-the-preservation-and-management.html> / UK<https://archetype.co.uk/our-titles/preservation-and-management-of-fluid-preserved-biological-collections/?id=440>). Here, the denaturant (methyl-ethyl-ketone) is also used as an agent and running medium in chromatography. In some cases, depending of the chemical make up of the pigments, colours can be surprisingly stable, e.g. as the red pigments in some formalin-fixed and ethanol preserved killi fishes. On the other hand, even black pigments - which are usually comparatively stable - can fade, as shown in the image below. The tissue sample in pure, undenatured 96% ethanol still looks pretty nice.

Supposedly, the key to the answer of Kelley's original question is/was the original storage medium and fixation/preservation of the specimen: if the colours are already faded prior to post-mortem fixation the results won't be as good as in preparations of freshly dead specimens, as John already said.

Also, the cellular set up of the tissue and its membranes surely have an influence on the preservation of the pigments in them (cf. marine vs. freshwater specimens), and also the concentration of the ethanol itself (cf. plate 7 in our book); left, jewel cichlids during stepping up to 70% EtOH, here, leaching of the red pigments starts when moving specimens from 20% to 40 % EtOH; haemoglobin and chlorophyll leaching out of specimens shortly after their transfer from 60% into 75% EtOH.

In my personal observation, the guanine (e.g. in fish scales - vivid silvery hue) appears to be more stable at 50-60%. The quality of the sealing of the container (= oxygen barrier) surely is a relevant factor as well.

Maybe this adds some useful thoughts.

With best wishes

Dirk

[cid:part1.p8YlspBg.MnSoJH6G at leibniz-lib.de]

[cid:part2.Ho4b6dcj.zPfWlNve at leibniz-lib.de]

Am 07.11.2023 um 06:44 schrieb Joachim Händel:

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

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>>> Simon Moore <couteaufin at btinternet.com><mailto: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<http://www.natural-history-conservation.com>

> On 6 Nov 2023, at 22:20, Cassidy, Kelly Michela <cassidyk at wsu.edu><mailto: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><mailto:simmons.johne at gmail.com>
> Sent: Monday, November 6, 2023 1:41 PM
> 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?
> [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 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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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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Stiftung Leibniz-Institut zur Analyse des Biodiversitätswandels
Postanschrift: Adenauerallee 127, 53113 Bonn, Germany

Stiftung des öffentlichen Rechts;
Generaldirektion: Prof. Dr. Bernhard Misof (Generaldirektor), Adrian Grüter (Kaufm. Geschäftsführer)
Sitz der Stiftung: Adenauerallee 160 in Bonn
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