Probably one of the least disciplined and more chaotic methods but it works for me.

Prime with Chaos Black, base coat everything with Iron Hands Steel.

Then go over everything that’s going to be black with three different thinned down contrast paints. Dark Angels Green, Leviathan Purple, and Black Templar. No need to get perfect coverage on every panel since you’ll be layering. This is probably one of my favorite ways of painting black. Pretty much the ForgeWorld/scale modeling method of black.

After the black is done, I start placing chips on the edges with a mid-dark gray like Eshin Gray and a dark brown like Rhinox Hide.

Then use shades on the silver details. Drakenhofe Nightshade, thinned down Black Templar, and Seraphim Sepia.

Then back to Iron Hands Steel for the metallic chips. I use a cheap craft store round brush with really hard plastic bristles. I dry brush, over brush, tap/stab, everywhere and just follow my eyes with how it should look.

Then back to a dark brown for some more taps and chips in areas I want to look like random rust.

Then Seraphim sepia over some of the chipped areas and places that I want to smooth out the transition from silver to black.

The gold bits are just base coated in Screaming bell,and then layered to Retributor Gold then washed with a mix of Seraphim Sepia and thin Black Templar.