Q&A about iPhone Finishes

A. I don't think the carbon will leach out of the surface, but some of the coating might be coming off. What happens is that the coating has been deposited with very high compressive stress. Initially, it is very hard and virtually impossible to remove, so the parts go out the door. However, with thermal cycling the high stress leads to cohesive failure of the coating. It might not be the entire surface that comes off, just minute flakes that stick to your fingers. Of course, some times the entire coating flakes off. In one particularly bad case a PVD coating was applied to putter heads. The heads were painted, bonded to the shafts, packaged, and air-shipped to Japan. when they arrived in Japan all of the coating had flaked off.

A. Adhesion of a coating is affected by the internal stresses of the coating as well of the substrate. For example, I find it easy to coat TiN on stainless steel but not on glass. But there is no difficulty in coating pure Ti on glass. Some electroplated substrates are difficult to coat. A common cause of poor adhesion is improper cleaning of the substrate.
In this case it appears there has been some powder formation during coating which has not been cleaned. You may wipe it with some solvent and see if the coating is completely removed. One can also do a tape test to check adhesion.
It is not necessary for the coating to contain carbon. In fact, it is not easy to deposit real black coating by PVD techniques.

Thank you, Jim. Thank you, _Prabhakara

A. Hi Manuel. Ruthenium is a conductive, tarnish resistant, precious metal. So it can be used, for example, for decorative black items; it might also be used in electrical contacts. Please introduce yourself and what you do, how you know that Apple uses ruthenium, and what inspires your question. There is too much lost motion in abstract questions and they immediately turn into stream-of-consciousness, making searchable organization of topics nearly impossible :-)

Luck & Regards,