You will find Silver, Copper, Gold and Chrome under Materials / Finishes. Bear in mind to that you can add new baseboards at the thickness/depth you want and finish them in brass or whatever you want. Keep double clicking on anything that looks clickable and you will be surprised what is hidden underneath. I don't recall a brass as such but you can set a paint colour that is close to what you want, double click the colour swatch and, (down the bottom) make it shiny. At the bottom of this same panel tick Display Setting Details. This gives you 4 sliders to change the shininess, brightness, transparency and colour bleed (haven't played with the last one yet).
If you play with a colour/texture with these controls it is best to add a copy of the colour/texture because the changes will occur anwhere you use this material. For example, if you set some fabric to semi-transparent for a lampshade and have the same fabric on curtains or chairs, then they will become semi transparent too - not a good look!! These effects can be applied to any material, so you can make walls transparent for example but it is only one way. To make it transparent from the opposite side you must change that too.
Allan