This is the response I received (from the makers of parylene):
Parylene will "dull" the luster of gold or silver. So I don't
I would like to run a test using a mirror finish gold substrate, and
report back my findings. I have several I can use but probably only
need one. "I don't think it will work" as opposed to "It will not
work" means I have a chance!
On two web sites I read that the coatings were optically clear.
"Parylene exhibits very little absorption in the visible region and
is, therefore, transparent and colorless."
I assumed that such a conformal coating would also deposit
uniformly, leaving no lumpy surface to scatter light. I ask myself,
"How lumpy could it be at 1.5 micrometer thickness?"