Did you know how to prevent the bluegrey color that's coming from jewellery?

I didn't know that before my friend Alexandra told me some week ago. That you can prevent the allergic reaktion thing that's coming from rings and earrings etc :o The bluegrey color.
You just paint your rings with nail polish, with clear nail polish of course. And it really works! But you have to remember, that you have to put on more really often because it tears off. But that's amazing! Why didn't I know this thing before? ;O
I use some normal nail polish from H&M. I think the price is 3.95€.