NOTE: The Blender 4.0 version has some slightly differences and improvements from what's seen below.

Documentation for Blender 3.6 or older:

Most node setups looks similar to the one below:

Only Brass and Bronze have extra color ramps. Brass has its own physically based color ramp already connected to the Principled BSDF. Since brass is an alloy of Copper and Zinc, there are also their two corresponding color ramps, mixed with a Darken Mix RGB node. You may want to use them to get different results, although I recommend only using the color ramp that's already connected, because that one is 100% physically based.

The extra Bronze material does not have its own physically based color ramp. Since it is an alloy of Copper and Tin, their two corresponding color ramps are mixed together to generate an approximate color value. This will usually provide an almost accurate value, although they will not be as accurate as the other materials.