[Nhcoll-l] Adding glycerin to & handling preserved soft inverts

[Simon Moore]

Hi Truth,

Yours is a slightly tricky enquiry but I have had some experience in this field when I was curating and conserving the NHM’s coelenterate collections back in the 1980s.

Firstly, The relationship between a jellied invertebrate and its preservative fluid is important as the two osmotically equilibrate over time, so each time you change the fluid or up the concentration of fluid, then you are temporarily upsetting that equilibrium; so unless the fluid is low in the jar or contaminated (not just coloured), try to leave them alone.

Assuming you wish to go ahead.
Firstly, you must make up all the diluted alcohols well in advance - alcohol and (purified but not distilled) water form a binary azeotrope when mixed - just an awareness, but more importantly, any dissolved gases in the fluids will be released when mixed.  So if you’re making up your 70% alcohol (presumably), the mixing must occur at least 24 hours before using or you will find many tiny air bubbles attaching themselves to your specimens (both outside and, worse, inside too!) resulting in floating tentacles &c! 

If alcohol dilutions have occurred and you wish to restore them to the required level, firstly check the specimen - is it still in one piece, reasonably robust? Do you want to proceed or leave it until the level drops further? If the alcohol concentration is below 30% you will need to increase the percentage up to the usual level by transferring through a ladder of increasing concentrations of alcohol at 10% steps.  This reduces the risk of osmotic shrivelling or syneresis, even though it’s a bore to do.  I use poly-propylene boxes with clip-on lids as containers for the ladder, and gently transfer the specimens up the ladder using a vegetable straining spoon (v useful).  Normally, a specimen takes about 2 hours to equilibrate in the new level of alcohol before being moved up again.
Your specimens should appear opaque rather than translucent if preserved in alcohol and will be slightly more robust than those preserved in aqueous preservatives.

If you add glycerine then this will increase transparency of the specimens (look better) but will give you an additional headache with releasing more air bubbles, an increase in osmotic pressure (laddering up more slowly) and you must ensure that the glycerine (usually 5%) is thoroughly mixed with the alcohol - any trace of Schleren Optics (wavy lines in the fluid) will spell out problems!

Finally, it’s fine to suspend specimens in jars: I use a thin monofilament with a small see-through acetate plastic disc attached by a knot in the thread, at the lower end. Sew this line through the umbrella (centrally) and then attach the end to the lid of the jar (some have a special glass knob for this purpose) or through the top-up hole if a flat circular lidded jar.  

Sorry to be so long-winded and cautious but these specimens are among the most difficult to look after.  I hope that the auto-correct hasn’t ‘corrected’ too much!

Let me know if you need any more advice and good luck!

With all good wishes, Simon

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

www.natural-history-conservation.com




> On 14 May 2021, at 03:48, Truth Muller <tmuller21 at coa.edu> wrote:
> 
> Hello All,
> 
> I've got two questions regarding preserved marine invertebrates, specifically fragile ones such as ctenophores, jellyfish, and larval crustaceans. The Dorr Museum is moving all of its collections to a new storage area, and we have a number of fragile specimens that have been neglected and need some "life" breathed back into them before the move.
> 
> 1. How does one go about "handling" preserved jellies and crustacean larvae? A few need new jars due to lid failure/cracked glass and I can't quite wrap my head around how to do it without ruining them. Our specimens are almost all preserved in 70% ethanol (a few old ones are in ~50% Isopropyl).
> 
> 2. I know I read somewhere that some amount of glycerin (I believe it was glycerin) added to the ethanol solution improves the way that jelly-like specimens "sit" in their jars, so that they don't just lie in a glob at the bottom. If that's true, how much glycerin should be used?
> 
> Any tips would be appreciated as always, thank you,
> 
> ~Truth Muller
> George B. Dorr Natural History Museum, College of the Atlantic
> Student Manager of Marine Wet Collections
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