This was a lot of fun. I don't have airbrush equipment but I was determined to give this a try.  I have some blank playing cards that I am using for my prompt cards and they have a shinny surface so I used them as my substrate. Jacquard Pinata inks in golden yellow, pink, coral and brass were used. I followed your technique of putting the metal into the coloured ink before blowing it with a straw. I found that the metallic grabbed the surface and did not blow well. I used a cotton swab to layout a path and then added the ink before blowing it. This gave some additional control but I found the best results by allowing a layer to dry and then adding another. Using the cotton swabs and rubbing alcohol (only 70%) I was able clean up the edges and any splatters. I added additional detail with an ink pen and a gold signo uniball pen. I will definitely try this again on different paper and at a different size.