Silver solder will withstand hot bluing process. You can blacken the silver solder line with Brownells "Silver Solder Black"
The trick to applying it is to attack the silver solder line immediatly after you pull the part out of the tank. Don't stop to oil it, just pull it from the bluing tank, into the rinse tank, and then; have a toothpick that has the tip presoaked in the silver solder black chemical. Rub it on the silver solder line only- don't go out onto the bluing if you can help it. I use about the same pressure you would use to write with a pencil, and rub it over each line 3-4 times. You may want to redip the toothpick and go over it again.
As soon as it looks passable, then oil the part. Bead blasted parts seemed to take this process better than polished parts.
We installed tons of silver soldered front sights on 1911's, Remington Rifle sights on shotguns (hey, it was the 80's) and Ed Brown Mag Wells this way.