[scale]

Hi Everyone,

I'm a middling blacksmith, and I've recently been investigating patinas for various metals--steel, copper, bronze, etc. My knowledge of chemistry is quite shallow, but I've been trying to relearn it so I can understand patination better--and maybe come up with some new effects someday.

I bought a sample for a "Copper Patina for Steel and Iron", sold at a blacksmith conference. There are two liquids, one clear blue and one transparent.

The clear blue clearly has copper sulfate pentahydrate in it--it actually says so on the label, and from investigating other patinas for copper and bronze, it is the same color.

The transparent liquid is listed as an "Activator Solution". It says it contains lactic acid and surfactants.

You apply the activator to the metal before the CuSO4 solution to get the reaction. You can also apply the activator to remove the copper patina afterwards.

CuSO4 in solution becomes ionic, and C3H6O3 becomes anionic, so I'm guessing that the lactic acid is the primary reactant in the activator solution? And if so, what is the role of the surfactant--and is there a way to tell what the surfactant(s) is? This last question is about safety--I know some surfactants are said to be endocrine disruptors.

But in general I'm just looking to understand this reaction.

Any thoughts?

[fledarmus]

I suspect the surfactants are there to remove any oils or dirt and allow the copper to plate out as a nice film over the steel instead of just floccing out.

What you are actually doing is reducing the Cu²⁺, which forms a nice blue solution, to Cu⁰, which is a shiny reddish metal, and chemically plating the surface. I suspect that the iron is oxidized, forming iron sulfates in solution, and the acid is a catalyst for the process.

[Enthalpy]

Agreed, this is a classical experiment with a nail in copper sulphate. Which also means that you can get the copper sulphate from more general suppliers.