[Nhcoll-l] Glycerol as a safer alternative to ethanol for display specimens - Feedback from your practice?

Fri Jun 27 06:26:22 EDT 2025

Thanks for this update Fabian,

If you could circulate the protocol that you mentioned on the list, many others would be glad to be aware of this (myself included).

Esther, when adding menthol or thymol, if you slightly tilt a smaller jar so that you can see the reflective surface of the glycerine, when you add the crystals you will see a thin protective film that spreads over the fluid surface as a barrier to prevent fungal spores germinating.

With all good wishes, Simon 

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

www.natural-history-conservation.com

> On 27 Jun 2025, at 09:57, Fabian Neisskenwirth <info at naturhistorische-konservierung.de> wrote:
> 
> Dear Esther, dear Marion,
> Sorry for the late response, very interesting topic indeed. 
> I have transferred a few collections into glycerol with very good results (i'm currently working on another collection doing this at the moment). My first try was done by a simple protocol that I got from Andries van Dam back in 2018, after he presented the use of Glycerol as a alternative preservation fluid at the PFC2018 in Paris. The use of glycerol goes back to the times of Carl Kaiserling (1869-1942) and Leonhard Jores (1866-1935), both German pathologists that presented their potential as preservation fluid over 120 years back in the field of anatomical preparation. Besides a few publications from Andreis van Dam (Maclead & Van Dam 2011; Van Dam 2020), there is not much resent research into this mater that i'm aware of. I will hopefully be able to publish something in a soon future. Andries and I did a nice presentation at a meeting organized by the German conservators/restorers society (VDR) last year, but there is no real conference paper available.
> 
> The glycerol solution concentration is crucial, specimens have to be transferred into a 65% solution of glycerol in water. By this, the mentioned absorption of humidity is inhibited since the solution is "saturated" with water and there should be no absorption of water from the environment. Glycerol solution with much higher content of glycerol (80-95%), can indeed absorb moisture from the surrounding environment, specially if poorly sealed. But if the transfer in steps into 65% of glycerol is made correctly, there is no need for any kind of fungicide in the preservation fluid. This is actually the biggest advantage of using glycerol in the first place (besides fire hazards, toxicity issues and/or evaporation), since it enables the use of a toxin free preservation fluid. Cleared specimens stored in higher glycerol concentrations, can be transferred into a 65% glycerol solution as well. Other mentioned issues like the slight color change, are of course things to be taking into account before the transfer. Besides that it is a really sticky job.
> Important things to take account are: big specimens that will take a long time to transfer from one step into another; a very good plan of transfer between fluids, since specimens will take different amount of time to transfer depending on their volume; the size of the receptacles for the transfer, since a good transfer requires a much higher ratio of fluid to specimen in order to enable a fast diffusion of the fluid; and of course the final container, since a good sealing is essential for the preservation of fluid preserved specimens. 
> I would be super happy to provide you with a protocol, even tough this has to be adapted to the specific collection, depending on specimen size, tissue type and so on. Just let me know.
> All the best,
> 
> Literature cited: 
> Van Dam, A.: Finding a cure for hazardous collections: the road to zero formaldehyde and ethanol. In: Collection Forum (34). 2020. S. 118–123. 
> Macleod, I.; Van Dam, A.: A migration mechanism for transfer of sharks from ethanol to aqueous glycerol solutions. Conference Paper. ICOMCC Lisbon 2011. 
> 
> Am 24.06.25 um 16:23 schrieb Esther Dondorp:
>> Dear all,
>> 
>> I was following your conversation out of interest and I am curious why you would not want to add a biocide to scientific specimens? Is it damaging? I ask this because we have our largest specimens in a tank in glycerol, because ethanol was no option (in terms of fire hazard and health and safety). And we added a lot of thymol to keep mold out...Also all the 'cleared and stained' specimens in the collection all have some biocide added to them.
>> 
>> Thanks!
>> 
>> Esther Dondorp
>> Collectiebeheerder reptielen, amfibieën en vissen
>> absent on Wednesdays
>> Monday, Tuesday, Thursday, Friday
>> 
>> 
>> 
>> 
>> 
>> - -
>> esther.dondorp at naturalis.nl - www.naturalis.nl
>> Darwinweg 2, 2333 CR Leiden
>> Postbus 9517, 2300 RA Leiden
>>   
>> 
>> Op di 24 jun 2025 om 16:12 schreef John E Simmons <simmons.johne at gmail.com>:
>> I agree with Dirk--without a very good seal on the containers, the glycerol will likely absorb moisture from the air, introducing both airborne contaminants into the containers and possibly causing them to overflow (I have had both happen to containers of specimens in glycerin that were not properly sealed). 
>> 
>> Because these specimens do not have scientific value, you should also consider adding a biocide to the glycerol such as a few crystals of thymol or a bit of camphor (as recommended by Simon Moore).
>> 
>> --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 Tue, Jun 24, 2025 at 9:40 AM Marion BILLOT <Marion.Billot at geneve.ch> wrote:
>> Dear colleagues,
>>  
>> I am currently working on an exhibition project involving fluid-preserved specimens, and I am exploring the possibility of replacing ethanol with glycerol for long-term display purposes. The main objective is to reduce fire hazards and mitigate health risks in display environments (cases that are not airtight).
>>  
>> I am preparing to present this proposal internally. As this practice is not yet established in my institution and tends to raise concerns, I would be very grateful for any feedback from professionals who have experience using glycerol in this context.
>>  
>> To clarify:
>>     • The specimens are of strictly pedagogical value, they are not scientifically rare or culturally significant.
>>     • We aim for long-term display in semi-sealed cases with limited air exchange.
>>     • I understand that transferring specimens from ethanol to glycerol requires several days of transitional baths in demineralized water to avoid osmotic shock and tissue damage. I am considering a gradual transition: ethanol 70 % → 50 % → 30 % → 10 %, followed by glycerol in increasing quart-step dilutions. I will let it in a minimum of 4 hours for small specimen (5 cm).
>>  
>> Have you used glycerol for display purposes in your institution? If so, under what conditions, and with what types of specimens? Any technical advice, protocol suggestions, or reference materials would be most appreciated.
>>  
>> Thank you very much in advance for your insights. They will be very helpful in supporting a safer and more sustainable exhibition strategy.
>> Best regards, 
>>  
>> Marion
>>  
>> 
>> <noname.png> <noname.png> Marion BILLOT
>> Collaboratrice support scientifique
>> Invertébrés
>> T. +41 22 418 6459
>> marion.billot at geneve.ch Muséum d'histoire naturelle (MHN)
>> Département de la culture et de la transition numérique
>> Route de Malagnou 1
>> 1208 Genève
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>> natural history collections to ensure their continuing value to
>> society. See http://www.spnhc.org for membership information.
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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
>> 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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> -- 
> Fabian Neisskenwirth
> Restaurator/Präparator
> 
> Waterfohrstr. 20
> DE-45139 Essen
> 
> Tel: +49 (0) 1573 2778729 
> 
> www.naturhistorische-konservierung.de
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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
> 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.