How was this shader made?

Koteeek

So here is the artwork from artstation https://www.artstation.com/artwork/Z5Ngl8 and i am very curious how was it textured like that. If you take a look there is only one texture for both paint and metal edge and i am interested how is it working inside the shader?
 

Eric Chadwick

Looks similar to the setup used here
Witcher 3 Blood and Wine architectural material
(thanks @Xguanabana for the tip!)

In the comments on Artstation they talk about using two channels of vertex color. 

More info about shader building, blending setups, and trim textures: 
http://wiki.polycount.com/wiki/MultiTexture#Modulation_Blending
http://wiki.polycount.com/wiki/ChannelPacking