"He who marches out of step hears another drum." ~ Ken Kesey
Frog, I have shimmer silver and when you lay it down it lays down silver, the little ink I have left is used in a 40 mesh screen and I can print over white, black etc. and the color stays the same it just adds silver glitter to the color. I too thought this should be easy to order but to my suppliers, they only have a silver shimmer or some type of ink that will change the color of what its covering. I'm not sure how to explain it no other way:(
I believe the overprint ink you are looking for is "Crystalina". Wilflex and Union have it.