I checked out Parylene from the link in the Orchid thread:
Is Parylene appropriate for preventing gold/silver/copper/brass alloys from tarnishing? I'm looking for something as invisible possible which would hold up over time. This would be for decorative objects on display.
This is the response I received (from the makers of parylene):
Parylene will “dull” the luster of gold or silver. So I don’t think
it will work for you.
Patrick Cleveland, Ph.D.
V&P Scientific, Inc.