These images were created with Houdini 9 and an image editor for the texture maps. The maps were added to an instance of a basic VOP network for the shaders. A render network was used with Takes to easily create multiple passes: Global Illumination (PBR), a sun/shadow pass (point light) and a Wren pass for the ink outline.
The compositing was done in Houdini with a Compositing network, in which the render passes are overlayed and modified with a colour saturation node. With the rendering and compositing networks both setup in Houdini the scene can be regenerated with 1 click of the render button.