I used enough of the merc compound stuff early on. Works great, but the trade off in health problems down the road is not worth it. You end up contaminating not only youself while doing the blueing but the area you're working in most likely.
There's just too many other formulas around that work well to use that stuff.
I use L/M now almost exclusivley. Slowing the rusting cycle down to 12 to 24 hours avoids the matted finish. It's an aggressive solution but lower temps & humidity slows it right down but it still rusts. I use it in the winter time with good but very slow results.
Mark Lee's formula for express blue works great for me. Sometimes I put a couple of coats of slow rust blue onto the surface and finish it up with express blue.
The Belgian Blue (Merc Compound) and the Brownells stuff just sit on the shelf. Pilkingtons works pretty well but I always go back to the Laurel Mtn it seems.
I use L/M for damascus finish to.
I tried the acid fume methods along time ago and that was a disaster for me. Others seem to have mastered it, but some say it doesn't produce a finish that wears very well. I'll never know!
The 'old' formula BirchWood Casey Barrel Brown used to produce a beautiful rust blue. A brilliant deep blue that was difficult to get with other available products. But it too was a merc compound formula and was taken off the market and reformulated some years ago to delete the mercury. I don't know if the new stuff works for rust blueing at all.
