the function of -70 for X-ray film

John R. Thompson jrt at
Sat Nov 11 14:21:49 EST 1995

Stephen Lessnick <stevel at> wrote:

>1)  Why would one expose 35S sequencing gels at -70 degrees in the first 
>place since they don't possess enough energy to make the enhancing screen 
>worthwhile.  On the other hand, soaking the gel in salicylate or PPO 
>would provide the enhancement effect, and then I believe it would make a 
>difference to expose the gel at -70.
Use of a screen is not the only reason to expose at -70.  The film
emulsion itself retains an image better at -70.  Thus irrespective of
whether or not a screen is used, there is advantage to be gained by
exposing at -70.

John R. Thompson
Merck Research Labs

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