[Tamlin]

One way to do it would be to select just the satin part (using your Selection tool of choice) and then add a Curves adjustment layer, with a sinewave-type curve. I've attached a zip file containing a preset curve that I've just made that gives you an idea - obviously you can tweak it to your own requirements. To install it, unzip the MetalCurve.acv file to somewhere on your computer then add the Curves adjustment layer. Click Load and navigate to wherever you saved MetalCurve.acv. Adjust the effect by dragging the points on the curve around, or adding new ones.

Attached is an example of the curve in use. I know it's a bit crude, but it was something I just threw together to give you an idea.