Howdy
I am not a chemist, nor an expert on gun bluing. But I can tell you that yes, some of the blueing done in the past was not as robust as modern blue. I used to have a Cimarron Cattleman with what they called the 'charcoal blue'. It was a throwback to some of the buleing done in the 1800s. It was a brilliant robin's egg blue, not the dark, almost black blue that we are used to today. And it was not robust. Within one year, the blue was completely gone from the backstrap of that gun, simply removed by the sweat of my palm. The backstrap had turned battleship gray. Probably it would have lasted longer if I had rubbed the gun down with an oily rag every time I put it away, but I didn't. By the same token, the blue on my Ruger Blackhawk that I bought brand, spanky new in 1975 has not worn at all, and it does not get rubbed down with oil either.
I have that old Colt in hand right now. I guess I exaggerated a bit when I said it has no finish left on it. It does. First off, Colt frames are Case Hardened, not blued. And the brilliant colors of Case Hardening will fade over time. That is a simple fact, the colors are beautiful, but they are not very robust. The colors can also be obliterated by strong chemicals, and even sunlight. The colors on the frame of that old Colt are almost gone, just some mottled remnants of the original case colors. The backstrap and trigger guard still have plenty of blue on them, except over 100 years of handling has turned much of that blue to a dark gray. Really a combination of blue being worn off and the underlying steel oxidizing. Not bright rust red, iron oxide can also appear dark gray. Which is the case with most of the rest of the gun; the barrel, ejector housing, and cylinder. A dark battleship gray where most of the blue has worn off and been replaced by dark oxide. Except in the cylinder flutes. Plenty of blue in the cylinder flutes, because they are protected from handling.
In fact, most of the time when you see a worn old gun, it is not 'in the white'; the color of fresh, unblemished steel. Mostly they are a dark gray, resulting from oxidation of the surface from years of handling. If a gun has been really mistreated, there will be pitting on the surface.
By the way, the reason nickel plating was so popular in the late 1800s; many companies produced more nickel plated guns than blued, is because nickel plate was more robust than some of the blues being used at the time.