A slightly fancier way to do patina or verdigris on copper coloured metals than just using Nihilakh Oxide.
Basecoat Brass Scorpion (I used Tin Bitz but similar)
Wash a mixture of Nuln Oil Gloss and Agrax Earthshade about 1:1. This keeps the pipes shiny.
Carefully glaze, and stipple, a mix of Nihilakh Oxide and Sotek Green at about 4:1. Add Lahmian Medium to thin before applying. Wash in recesses, but wipe most off the brush before stippling or glazing other areas. USE GOOGLE IMAGES FOR REFERENCE!
Build up the effect by applying smaller dots and washes with a mix of Nihilakh Oxide and Baharroth Blue . This is about 2:1. Again, thin with Lahmian Medium .
Apply, finely, some Nihilakh Oxide . This can build colour in areas you like, and I applied over the brighter points of previous steps.
Tidy and build up the copper layer with Brass Scorpion , then Sycorax Bronze . Stipple dots on, and you can also glaze the Brass Scorpion layer over any overly green bits. I also added some thinned Coelia Greenshade to bring together the patina. This was stippled in some areas.