Question: Cold blue

[Dave London]

Anyone know why cold blue stains 24 kt gold

 

[mitch]

without digging up my bottle, iirc, cold blue is usually some mix of selenic(?) acid and while 24K is almost impervious to most acids i'm guessing it can oxidize the surface ever-so-slightly before the reaction peters out? somebody once told me iodine stains gold, too, but i'm not sure why anyone would be using that for anything?

 

[Adder]

Dave, I have no clue, but when I used my 30 year old bottle of Cold blue on my gold, the gold surface turned from yellow to green colour)

 

[graniteguy52]

Dave,
Some of the cold blue solutions contain copper selenide. I'm guessing the copper reacts with the gold causing the coloring. (It has been way too long since high school chemistry to be sure of that)

 

[JJ Roberts]

Brownell's gunsmithing supply sells a bluing solution Classic American Rust Bluing Solution,very easy to use and will not effect the color of gold or silver. J.J.

 

[jerrywh]

I have had this problem also. I'm inclined to think it doesn't stain the gold it plates it with copper sulfate. Can't prove it though.

 

[SamW]

I expect you are right Jerry. Herter's Belgian Blue will coat gold with a wash of mercury which amalgamates with the gold...yes, the solution has some form of mercury in the formula. Nothing like very bright silver color for your gold!!

 

[mitch]

I expect you are right Jerry. Herter's Belgian Blue will coat gold with a wash of mercury which amalgamates with the gold...yes, the solution has some form of mercury in the formula. Nothing like very bright silver color for your gold!!

I LEARNED THAT THE HARD WAY ABOUT 35 YEARS AGO!!!!!!!!! I used to do my own rust bluing and the parts came out of the tank and I thought, "WHAT THE FUUUUDGE???"

If any of you don't want to learn from my experience, you'll be needing this next bit of info:
Put the newly 'silver plated' parts in an oven at 350deg. for an hour or two, which will vaporize most of the mercury. NEED I ADD THIS SHOULD BE DONE WITH GOOD VENTILATION? Then when the parts cool, rubbing them with a pink drafting eraser should return them to their previous yellow glory.

 

[SamW]

Same as you Mitch, about 35 years ago (or more) but I used a propane torch with a light breeze from left to right and painted the flame across until the merc was gone. Almost had heart seizure at first!

 

[Dave London]

Thanks everyone,lot of excellent information here.
Ventilation HUM don’t need no stinking ventilation

 

[DKanger]

That old bluing had mercuric chloride in it. None of the blues offered today contain it as it was banned as a health risk many years ago......for obvious reasons. I've still got a couple of bottles of Birchwood Casey blue, but the MC has crystallized and fallen out of suspension.

 

[gcleaker]

I LEARNED THAT THE HARD WAY ABOUT 35 YEARS AGO!!!!!!!!! I used to do my own rust bluing and the parts came out of the tank and I thought, "WHAT THE FUUUUDGE???"

If any of you don't want to learn from my experience, you'll be needing this next bit of info:
Put the newly 'silver plated' parts in an oven at 350deg. for an hour or two, which will vaporize most of the mercury. NEED I ADD THIS SHOULD BE DONE WITH GOOD VENTILATION? Then when the parts cool, rubbing them with a pink drafting eraser should return them to their previous yellow glory.