it's actually quite easy nia.
as i said la, this technique only applicable to small areas. so the parts i painted on SF still ok. Not applicable for wide areas like armor plates/shield etc.

here's normally what i do la. mix 1:1 ratio of gold + thinner. just paint the whole area u wan. wait dry, paint again to at least cover most of the area. u'll see some brush strokes but it's ok

next, no need dilute with thinner, just paint gold straight on to the area. again i must stress tht only applicable for small area. usually takes about 2~3 layers to make it look nice and even.

so far, i can confirm this technique works for gold and silver. others i can't because, it's hard to paint it uniformly :/

u shud try on blank runner trees before u proceed on your SF.
on 1:1, u'll see it's sorta dilute and got brush stroke.
on straight paint, u'll see the strokes begins to be covered, but also slightly more hard to paint becos it's thicker.

NOTE: between each painting step, remember to wait for paint to dry D:
i just use some cheap ass brush and normal thinner. works for me