I received this email:
I would like to know when titanium and gold accessories are worn together, will there be any chemical reaction affecting both metals. I am wearing a Gold Chain now and I wish to purchase a Titanium Chain but I do not know whether there will be any adverse reaction. As I know Gold and Silver accessories can’t be worn together, so how about titanium and gold?
I hadn’t previously considered that gold and silver might react on the skin. But, yes they do. It isn’t much of a reaction, but it is to the detriment of the silver.
Titanium is safe to wear with other metals.
Titanium always has a protective oxide coating that prevents any electrolytic reaction with other metals. Basically, moisture cannot reach the metal itself in order to complete a reaction. If it is scratched, the protective coating immediately re-forms (unless in a perfectly inert atmosphere (argon, krypton, etc) or a vacuum). That’s part of why titanium is such a good candidate for medical implants.
Go ahead and try it: http://mrtitanium.com/TitaniumChains.html
In detail, any two metals in a conductive solution (impure water) will exchange ions. If the metals touch, then an electric current forms, eating away at one of the metals. That’s how a battery works. Body moisture acts as an electrolyte between silver and gold, and hydrogen is produced at the gold side, and oxygen on the silver. Silver oxide is black and soluble; it tarnishes and eventually eats into the silver.
But for the reaction to continue, neither metal can be allowed to grow a continuous, non-soluble insulating layer. Titanium and niobium grow very good insulating layers when just exposed to most electrolytes. In fact, I force this insulating layer with enough voltage to produce the colors. That’s called “anodizing.”