Hello Laura,
Thank you for posting this question! I am the acting C2C Monitor this period, however, I have not (thankfully) encountered gum on collection material. I am hoping others might weigh in on this.
I think it is prudent to remove this soon. The gum will attract debris, pests, and I imagine people will touch it and smear it over more of the surface (ew). Gum does become brittle over time and it may be able to be knocked off with a small spatula. When using a tool, be cautious as to not affect the wood surface -- popping off smaller areas will be tedious but you'll have more control. Cold may cause it to be become more brittle, though you'd want to chill it without adding moisture (I would pop ice cubes in a bag and apply it over a small working area). However, this is something I would try on my regular, not historical, front door. Good Luck! and maybe someone will experience will give specific advice.
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Elizabeth Stone
Connecting to Collections Care Monitor
Collections Conservator
University of Iowa Libraries
Iowa City IA
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