Talino,
It is not so difficult as you might think. I will give you some options but there are many more.
Most at the time i mix my printers inks with some turpentine. Then let it dry for a few days.
After drying i take put some little pure ink on the surface that's to be need the highlight.
When it is gold, i mix this with silver printers ink to high highlight again after drying.
Marc