First, I compared the colour to my OC Burnished Gold, and the mixes with black I have made to paint ancient gold. I was surprised - and delighted - to see that it was an almost 100% match to the mix with a few tiny drops of black.
Then I painted a censer/ball-and-chain/whatever on the mini I'm currently working on
- Charred Brow
- Burnished Gold with black (dark mix)
- Polished Gold
- Burnished Gold + Mithril Silver
Polished Gold covers much better and smoother than the Citadel metallics (apart from Mithril Silver, which is still a fabulous paint to work with).
If the rest of Vallejo's metallics are just as good, I'll have to get more!
I think my Burnished Gold will be transformed into an even darker mix by adding black. I don't like the finish of it very much, anyway, and it does not cover too well.