Hi John, 10% neutral-buffered formalin is the most common fixative used for histopathology and allow storage for long periods of time. However, sampling of tissues most be small and thing to allow for fixative proper fixation. Best preservation is using percussion rather than immersion. In human pathology vs experimental samples collected are larger, left on the fixative for longer time and trimmed before processing for paraffin embedding. Here a link with information that may help

https://www.thermofisher.com/ca/en/home/life-science/protein-biology/protein-biology-learning-center/protein-biology-resource-library/pierce-protein-methods/fixation-strategies-formulations.html

Hi John, the advise of Olga is incomplete as prolonged fixation is not advisable for long duration. My advice, you should divide your specimens into 2 parts. First wrapped in foil and labeled by a serial number and immediately freezed in liquid nitrogen then in deep freeze -20 degree. The second fixed in 10% neutral-buffered formalin and processed as paraffin embedded blocks for storage forever (good morphology with reatined many antigens),

John,

For standard histology, it's hard to beat 10% neutral buffered formalin.  Olga's suggestions above are excellent.  However, in my work at Harvard Museum of Comparative Zoology, I do histological and histopathological work on specimens that were preserved simply by immersion in formalin more than 100 years ago.  Most of these still yield very good results.

Good luck.

Bruce

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