Varnish and Mildewcide
 

Folks, I use epifanes gloss and it's rather good in a lot of ways.
One problem that does appear in some spots is blackening, which I
assume is mildew.

I wonder if there's any mildewcide included in common varnishes, or
that might be added safely. I googled for it, and the only one that
showed up is "Circa 1850 Exterior Varnish " retailed by Jamestown.

Any words of wisdom here?

AS