[Nhcoll-l] Shark gunge!

[Simon Moore]

Hi Alina,

Thanks Lex for passing this on.  
Your problem with opaque white goo cannot be readily ID’d from the photo’s but it might be due to polymerisation of the formalin into para- and meta-formaldehydes, particularly if the temperature drops to below about 10 deg. C during the year..  This appears as a misting at first and then  develops into a crystalline solid that envelops / encrusts the specimens. This is soluble in methanol but may take a week or tow if a specimen is severely encrusted.  However, your specimens did not look as though they had this problem but it’s a thought.  Addition of 10 ml of methanol per 2.5 litres of formalin fixative should prevent this.

Scenario 2 may be due to inadequate fixation where big specimens are not sufficiently perfused with formalin by injecting it into the internal organs and body cavities - I presume that this was done.  Also test the pH at regular intervals (a colorimetric strip is fine); the pH can fluctuate if there is some adverse reaction occurring and if the pH starts to drop then this shows that something adverse is occurring such as lipid content levels (from the liver) may be increasing and oxidising.  Bear in mind that formalin will only preserve lipid but not fix it, so chemical changes in the lipids can still occur.
Protein breakdown can also occur at low pH levels (below 5) and this can lead to gelatinous semi-opaque deposits and is particularly noticeable with livers from animals that have a ‘varied’ diet (pigs).
Tests the pH first.

Apologies if none if this is new to you but I hope that it helps.

With all good wishes, Simon.

Simon Moore MIScT, RSci, FLS, ACR
Conservator of Natural Sciences and Cutlery Historian,
www.natural-history-conservation.com 




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