AS I recall, Silly Putty had a fairly greasy base since I used to lift cartoons from the newspaper with it all the time and there was always a greasy stain left on the news print.. Residue on fingers could leave fingerprints on the emulsion side if not VERY careful and using it on the notch should only be done on the back side so that nothing touches the emulsion. Otherwise, there could be serious problems with oils blocking the developer wherever the stuff touches including from the fingers.
I think the paper and pencil idea is much safer.
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