In general, a good color to prepare for silver (leadbelcher) is black, and a good color to prepare for gold (Balthazar gold) is brown. This is because acrylic silver and especially acrylic gold aren't 100% opaque, and black and brown are preferable to be the color underneath, rather than, for example, white, green, blue or red.
Now, specifically, I assume that you want to achieve the shades of gold and silver used in the
GW studio models for demigryph knights:
http://www.games-workshop.com/en-CA/Empire-Demigryph-Knights
I like using abbadon black and rhinox hyde as the prep colors. This also helps me identify during the basecoat stage what metallic to use.
Moving past that, the silver is very easy to achieve. Almost all
GW silvers follow one of two patterns:
- For duller silvers, like swords and bolters, simply base coat with Leadbelcher, wash Nuhln Oil, and edge highlight Runefang Steel highlights.
- For brighter silvers, like plate armor (Demigryph Knights' plate) base leadblelcher, wash Nuhln Oil. Then layer Ironbreaker, but leave the darkest recesses untouched. Finally, edge highlight runefang steel.
Gold is trickier. It's important to recognize that
GW golds are divided into yellow (pure) golds, reddish golds, and brassy golds. The banner lion
If you look at the blowup of picture #2 on the Demigryph link that I put above, you'll notice that the banner lions are a more yellowy shade, whereas the armor plates and helmet wings are a more reddish gold.
For the armor plates, basecoat with Balthazar gold. Paint a layer of Gehenna's gold over the entire area that you had Balthazar. This will leave you with a very reddish gold.
Now, wash the gold. You have a few choices: Seraphim Serra, Reikland Fleshshade, or Agrax Earthshade will all create depth and fill in recesses. I suggest Seraphim Serra (Agrax is too dark/brown; Fleshshade not dark enough). Cover all of the gold with the wash.
Once the wash is dry, layer Gehenna's gold over it, but this time, leave the recesses -- again, on the blowup of picture #2, this would be the darkened areas, like around the eyes and beak area, and the detailed recesses on the iconography, and around the studs.
Next, very sparingly, paint highlight raised areas with Auric gold. Auric isn't red at all (but it's quite bright), so be careful not to overuse it. Finally, you'll notice in the photograph that there are some areas that really pop out with the glint of shininess. On these areas, which are generally raised corners, use runefang steel, again, sparingly.
Now, the chord: It should technically be possible to do exactly the same thing for the chords. However, I never have luck with this, because what happens to me is that my washes are not 100% consistent, leaving some of the chord recesses lighter or darker than other parts. it's not easy to fix.
So, what I do for chords is that I paint Warplock Brass (the darkest metallic base in the
GW line), wash it immediately with agrax earthshade or seraphim serra, and then layer, one twist at a time, with Balthazar gold. Then, with a finer brush, I layer Gehenna's. I just find it easier (for me) to paint the recesses really dark metallic, and then lighten each twist -- otherwise, it just turns out inconsistent, which drives me nuts.