[Nhcoll-l] Fluid Preserved Specimen - Transfer From Formalin to Ethanol - Seeking Advice on Using a Vacuum for Air Trapped in Specimen

[Simon Moore]

Hi Jaclyn,

One question - was the 20% alcohol already made up to that concentration well before the specimen was placed in it?  Reason is that diluting alcohol with purified water will generate a small exothermic reaction that triggers the evolution of many tiny air bubbles - not quite like champagne but similar.  If the alcohol was diluted well before the immersions/transfers took place , then it’s likely to be an osmotic reaction but for densely-muscled specimens like fish, this is unusual.

By placing ‘aerated’ specimens in a mild vacuum, this is enough to swell the trapped air so that it seeks an exit point.  If your fish can fit in a beaker that itself will fit into a vacuum desiccator, then this can be done.  Be careful if you’re using an oil-filled pump, to shut the valve connecting the desiccator to the pump before switching off the pump or the vacuum from the desiccator will suck the oil from the pump out into the desiccator.  Do a ‘dry run’ with a beaker of water first, so that you fully understand the method.

With all good wishes, Simon 

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

www.natural-history-conservation.com



> On 23 Jan 2025, at 20:16, White, Jaclyn <JaclynWhite at therooms.ca> wrote:
> 
> Hi everyone,  I am currently transferring a fish specimen from buffered 5% formalin to 75% ethanol. I have been following the instructions in Fluid Preservation – A Comprehensive Reference to stage them through ethanol concentrations (20/40/60/75). After placing the specimen in 20% ethanol concentration, it appears air has been trapped within the specimen and the instructions are to place the specimen in a vacuum to remove the air.  Has anyone here had experience using a vacuum for this purpose? Does this typically occur at the first staging step? If the specimen has been in 20% ethanol for over 24 hours and I complete the vacuum step, do I need to start over at 20% or can I move directly to 40%?
> Any advice would be greatly appreciated.  
>  Thank you in advance,
>  Jaclyn White | Natural History Collections Intern Archives and Collections Department The Rooms – St. John’s, Newfoundland
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