I thought it would be so easy! :-)

I want to put a gold monogram on a transparent object so I came up with the idea of a rectangular layer on a transparent shader. I thought I would create a multichannel mixer on it using a reflective gold in one source, nothing (multichannel mixer with each channel set to none) in the other source and my bitmap of a monogram as the blender but no matter what I can get only the surrounding area gold but never the letter itself. I've tried "invert" and tried a black on white bitmap and tried reversing the sources but nothing gives me the desired result.

Could someone help?

Thanks
Ed