I'm not completely sure how well it would work on pewter, but the best way I've found to get a genuine blued look, on zinc alloys at least (even with polished parts), is Brownells Oxpho-Blue:
BROWNELLS OXPHO-BLUE® | Brownells
It's not super easy though, what I did is diluted it 5-parts hot/warm water to 1-part Oxpho.
Then the process I used was in this order: I degreased the parts thoroughly by dipping and scrubbing in denatured alcohol with a soft horse-hair brush, then dipping and scrubbing the part while submerged in the Oxpho, then dipping and scrubbing yet again in clean water to stop the reaction. And then I repeated the whole process over about 10-20 times to build up a nice even finish.
It will come out looking matte-black at first, but you have to 'very' lightly polish off the surface with very fine polishing paste, either model polish or super fine automotive polish works.
The reason I went that direction was because on zinc, using it non-diluted cased it to have sort of an underlayer reaction that showed through as different shades of brown/tan and not very uniform when viewed in good lighting.
Ever since I've used Oxpho-Blue, I haven't really touched Birchwood Casey stuff since. Unless I'm going for a matte finish like aluminum black gives. Their products are way too corrosive on most metals.
Here's an example of a Tomenosuke Blade Runner Steyr receiver I finished using the same method, although with this one I heavily polished the part beforehand:
-Carson
Speaking of DEC scope mounts and dovetails...
I have one of the newer runs from last year, with a pewter mount and no dovetail. I think I’ll scribe a dovetail seam on both ends.
But I have a question for anyone who has a similar mount: How do you color it? Aluminum blue has brought it to a mottled, color case hardened look, but no further. Steel blue doesn’t touch it. I’m using Birchwood Casey chemicals, but is there a better way? Or is paint my next best option?
Thanks in advance for any advice!