[Nhcoll-l] [EXTERN] Removing specimens from formaldehyde

Mon Sep 30 14:28:11 EDT 2024

Dear Vanessa,

There is a very simple way to monitor the progress of fluid exchange when transferring specimens from an aqueous solution of 4% formaldehyde to 70% ethanol.

Since the density of ethanol (d=0.79) is much lower than the density of water (d=1.00) and the density of buffered formaldehyde 4% (d=1.02), during the time the specimen is in one of the transfer baths (ethanol 20-40-60-70), the density of the surrounding fluid will slowly rise due its exchange with the heavier fluid inside the specimen.

When measuring the surrounding fluid periodically (e.g. once a week) with a densimeter you will see a logarithmic decrease in density until there is hardly a significant change anymore, which indicates that the transfer step has been fully completed and the specimen can be placed in the next bath. This way of monitoring will ensure correct transfer times without having to worry about the variables of type of specimen, shape, size, etc.

Like Dirk and John, I would also recommend four baths, but with slightly different concentrations: 30-50-70-75, which gives after complete exchange an end concentration a little over 70%.

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)
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Scientific associate | Natural History Museum London

________________________________
Van: Nhcoll-l <nhcoll-l-bounces at mailman.yale.edu> namens John E Simmons <simmons.johne at gmail.com>
Verzonden: maandag 30 september 2024 17:55
Aan: Dirk Neumann <d.neumann at leibniz-lib.de>
CC: nhcoll-l at mailman.yale.edu <nhcoll-l at mailman.yale.edu>
Onderwerp: Re: [Nhcoll-l] [EXTERN] Removing specimens from formaldehyde

Vanessa,
Dirk's advice is correct.

The reason we lack reliable recommendations for soaking time for each step is that there are too many variables to consider, such as the surface-to-volume ratio of the specimen, thickess of the specimen, whether the specimen has thin skin, scales, fur, a shell, and so forth, and the density and structure of the dermal layers and internal tissues.

There are several papers that give penetration times for formaldehyde or ethanol, but these rates should not be extrapolated for whole specimens. All of the published penetration rates   that I have reviewed  are based on small samples (often no more than 1 cubic cm in volume) of gels or agars, etc., so the penetration rates are not transferable to whole organisms. For example, the penetration rates of formaldehyde published by Steedman (1976) are based on gelatin and casein gels, Medawar (1941) used plasma clots, and Baker (1958) used gelatin/albumin gels.

The rate of penetration of fixatives and preservatives is complicated by the fact that the chemicals modify the tissues as they penetrate them, which greatly impedes the rate of penetration of more of the fluid, and quickly limits the depth of penetration of the fluid (this is why it is recommended to inject formaldehyde or other fixatives into specimens). In addition, penetration rates of preservative fluids are temperature dependent.

I hope that someday we will have enough research on penetration, fixation, and preservation rates that we can come up with some general guidelines for time required for each soaking step, but until that day comes, Dirk's advice is the best we have.

--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, Sep 30, 2024 at 11:30 AM Dirk Neumann <d.neumann at leibniz-lib.de<mailto:d.neumann at leibniz-lib.de>> wrote:
Dear Vanessa,

rising and staging times depends on the size of the specimens and how readily superfluous the formaldehydes is diluted from them. The specimens shown may require 2-3 days of rinsing, and then slowly going up 20/40/60/70. Each of these steps may take 1 week or longer, it depends how much formaldehyde comes out of them.

All together you should assume at least a month, but it can take you longer.

With all best wishes
Dirk

Am 30.09.2024 um 17:14 schrieb Vanessa Pitusi:

Dear all,

Recently, I have discovered that most of our larger specimens kept in the large collection jars, are kept in formalin (photo for reference).

I have looked into removing the specimens from formalin and placing them into ethanol. I understand the steps that have to be taken, but I was wondering if anyone has advice on the soaking time for each step. That is the only thing that is kept vague in the texts that I have read. One reference mentioned that tortoises and racoons take two to three days.

Most the specimens that I will work with a large fish, cephlapods, and birds.

In case any of you have done this, any advice on this or the process is appreciated!

I am also open to having a quick chat via Teams or Zoom.

Kind regards,

Vanessa

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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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NHCOLL-L is brought to you by the Society for the Preservation of
Natural History Collections (SPNHC), an international society whose
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