Here is the map I used (although it's half size here, otherwise it was kind of big). I created this from some photos I took and mashed together to create a nice crusty grunge map. It kind of looks like the Shroud of Turin but it's just some pictures I took while walking by buildings, etc.
The gold material uses two bsdf layers, one very sharp the other fairly rough (I think 40%). The sharp layer uses and IOR value coupled with an extinction value (n.225 k2.95) or something close to that. Those are actual measured values I found on the interwebs.
The rough layer I just used a high Nd value (40). The mix between the two is 100/10 with this grunge map used in the rough/10 layer.
And for the sake of laziness I just applied it using cubic mapping.
GoodScratch01-half.png [ 446.63 KiB | Viewed 259 times ]