If you are worried about your "regular" water baths evaporating
(which wouldn't happen if filled satisfactorily full and covered as
Gayle suggested) you can purchase "molecular" grade waterbaths just
for this type of purpose. We do in situ hybridizations etc using them
overnight - sometimes even several nights without any issues. When
filled with enough water, they hold their temp wonderfully and with a
lid there is not that much evaporation.
Even so I routinely do overnight incubations for retrieval at 80 degC
and haven't had any issues, but my water baths are quite deep and I
fill them rather full before use. I weigh down my plastic slide
container (the Tissue tek kind that holds 24 slides) with a weight
and all is stable for the night.
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