Cheers John -
They are bronze. I have tried mightily to get bronze acorn nuts but cannot find them.
What are the portlights frames made of? Aluminum, stainless, plastic, bronze, chromed bronze?
If bronze, I would stick with all silicone bronze hardware (nuts and bolts). If chromed-bronze, all stainless hardware would probably look better. There must be a source for s/b acorn nuts since we have them on our boat and I've often seen them on others. Hamilton MArine might have them, but my first look would be at Jamestown Distributors.
Edit: As for the interior of the portlights being dry, in theory yes. However, if you are installing solid bronze, through-bolted portlights, be aware that the interiors will "sweat" when there is enough interior/exterior temperature gradient. These portlights conduct both heat and cold, so in the winter will feel quite cold to the touch, leading humidity (from our breath and/or the propane stove) to condense on their surface.