Doug,
Welcome to the Grumble!
It is a bit eerie that I saw your post immediately after taking in a hand colored etching to be rematted and reframed. The etching is titled, "Hastings from the Sea" and is verified to be circa 1872. It is a truly beautiful specimen of hand coloring on an original etching!
Now for the bad news, it was matted and framed in your home town!! (That is still some good news.) It is ATG'ed to a piece of regular postermount board and has 2 paper mats on it! (THAT'S the bad news!!) It was done by the "Royal Mile Gallery" on the Royal Mile in Edinburgh.
Now how ironic is that??
Regarding your question about frame finishes, there are so many finishes on the market here in the States and I wonder how many of them would be accessible to you across the pond? Of course, there is the traditional gilding in either gold or silver or metal leaf but that does require some advanced skills that aren't readily picked up online or in a short workshop.
Paints of all kinds can be used to color, tone, antique, and otherwise impact a bare wood frame. High gloss, semi-gloss, and flat colors all work depending on the individual situation.
Wood stains are popular here. I don't know how they stand in the UK but there are solvent stains, water based stains, urethanes, powdered stains, stains and finish combined, etc. It would be a hard guess to recommend to you one over another not knowing what you have access to in the UK.
I know this isn't much help but I just had to post after I saw the very first thread that I looked at coming from the town that had framed this piece that I took in not 20 minutes ago!!
Framerguy