The trick is to find a couple of areas that are to receive bright highlights. The picture below shows the dialog immediately after the Smooth button was used. In order to make it more exact in following this, just load the Silvery. ArbMap file via the Open button right in the Arbitrary Map dialog. Notice that the logo shape itself got mangled in the process, including all kinds of ugly artifacts near the edges.
Life is like that, too.
Here the mask is the black shape that cuts out the gold from a previous document. In a case where the two are not necessarily touching one could use two masks, one to cut out the gold and another to cut out the silver background. It seems cumbersome, but those 3 steps can yield extremely complex and ultra clean pictures and it is still light years faster than any manual touch up, or trying to rope in the parts via selections and then pasting. Before and after the Gaussian Blur filter What we need to accomplish with this is to add more transitional grayshades to the mask, so that where it used to jump from black to white, it now steps through dozens of shades. Life is like that, too.