[Nhcoll-l] Precipitate or Mold in Ethanol Stored Specimens

[Simon Moore]

Many thanks for this information - it is just what I am lecturing about in Paris next week to raise awareness of this type of problem!

I have often been asked to ID crystal growths and suspensions in fluid-preserved material and the answers (If there are any) are as varied as are the causes of their appearance. 

Firstly I often dilute concentrated formalin to the standard 10% fixing strength using local tap water, this offers and usually maintains a neutral pH  (7.0 or just a bit below 6.5).  If tap water is used to dilute alcohols of any sort, to preservative strength (70% or 80%) then this produces a precipitate, usually with 24 hours of mixing.

Where fluids combine with animal and plant material during the fixation and preservation stages, they often leach solute by-products into the fluids.  Over years the fluid and specimen build to an equilibrium and assuming that no lipid leaching or similar contamination occurs (the cholesterol for example but isn’t this partly soluble in alcohol?), then this can go unnoticed until the jar is topped up with fresh preservative fluid and then a snow-dome effect can occur - looks terrible but the specimens are undamaged. Once the ’snow’ has settled and the fluid has cleared (or partially) one can see the effect (if any) this change may have brought about on the specimens but usually it’s slight or no change at all.

Crystals of calcium stearate have been analysed (by FTIR) adhered to specimens - how does that come about?  The causes and results can be quite bewildering but a record of treatment/s to specimens is most useful.

Mould (I’m a Brit!) will only start to appear if the concentration of alcohol falls below 30%, similarly it can grow in formalin at c. 2-3% concentration (0.8 - 1% formaldehyde) - these are the critical parameters for mould growth and (it appears) that only certain species of mould can grow in these conditions.

If anyone has any further thoughts I would be most interested (I only have a week!)  Or examples of weird looking contaminants attaching to fluid-preserved material please post these to me off-list but not too many!

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 Nov 2018, at 19:23, Lazo-Wasem, Eric <eric.lazo-wasem at yale.edu> wrote:
> 
> Hi Alex,
>  
> This is what happens when a specimen fixed in formalin is not rinsed sufficiently in water before immersion in alcohol.  Depending on the size of the fixed specimen, one needs to wash the specimen for anywhere from a few minutes (small crustacea) to several days (large long fixed sponges, fish, etc.).  I’ve never tested like Judith Price mentions, but the person who hired me several decades ago cautioned me to rinse specimens in water before transferring to alcohol else I can expect precipitate.  It happened enough that I believe his cautionary note without understanding the chemistry.
>  
> Best, Eric
>  
> Eric A. Lazo-Wasem
> Senior Collections Manager
> Peabody Museum of Natural History
> Yale University
> 170 Whitney Ave.
> New Haven, CT 06520
> 203 432-3784 <tel:203%20432-3784>
>  
> From: Nhcoll-l <nhcoll-l-bounces at mailman.yale.edu> On Behalf Of Alex Krohn
> Sent: Tuesday, November 27, 2018 1:53 PM
> To: nhcoll-l at mailman.yale.edu
> Subject: [Nhcoll-l] Precipitate or Mold in Ethanol Stored Specimens
>  
> Hi everyone,
>  
> I recently found some bizzare white granules in some our ethanol preserved specimens. See the attached photos. The white granules tend to stick to the items in the jar, rather than rest at the bottom of the jar. They do not crush easily (like I imagine precipitates would), but instead squish more like tiny styrofoam bits or pieces (like I imagine mold would).
>  
> Has anyone seen this before? I washed the specimens and jars in fresh 70% EtOH, and then replaced the EtOH in the jar. So far no new granules have appeared. If anyone has any better ideas of what this might be or how to treat it, I'm very interested.
>  
> Thank you!
>  
> Alex Krohn
>  
> ---------------------
> Assistant Director
> Kenneth S. Norris Center for Natural History
> University of California, Santa Cruz
>  
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