If it actually appeared to darken, it might be the light you are viewing it in or it might be oil wetting. I'd try degreasing a spot and see if that makes it appear more blue.
I have had great luck with the Birchwood Casey re-blueing kit i bought it at the local hardware store for $13 turned out great and had enough to do about 2 to 3 rifles comes with complete and very detailed instructions and was very easy.
Too coarse blue absorbing oil will turn black. If you want blue, there is no fix except to remove the blue and start over with better metal preparation and strict attention to directions.
Even so, Belgian blue will do a better job and last longer than any cold blue. None of them will last more than a short time if the gun is handled at all, no matter how good it might look when first done.
Even so, Belgian blue will do a better job and last longer than any cold blue. None of them will last more than a short time if the gun is handled at all, no matter how good it might look when first done.
Thanks for the answers. They belong to a friend and he was just
wondering if he did something wrong like gun cleaning solvent or
something else after he was finished. It took a fairly long time to
darken.