I printed out the digital lines, and transferred them to Arches watercolour paper using pastel pencil on the reverse of the printer paper - I scribbled out a layer of pastel, then turned it over and, using a pen to press down on it, traced out the lines. Much careful inking then followed; I'm using Daler Rowney FW Acrylic Ink here - a mix of sepia and black, diluted accordingly. Inking is therapeutic. There are few things more soothing than the sound of a brush going over paper, and the physical motions of making careful strokes. I loved drawing the map. But I managed to ink the face wrongly!
Thankfully, there's Photoshop.
I then laid down more ink washes to establish values on the piece, as much as it pains me to paint over those map lines. Next, I scanned the piece in portions, then stitched it using Photoshop's File > Automate > Photomerge command. The next big part to tackle was adding colours, layer after layer, making use mostly of Multiply, Overlay, and Screen modes. Justin Gerard's post on Muddy Colors here goes over the basics and I highly recommend reading it.
And Prunella's face gets redrawn! I sample some of the paper texture from the background to ensure that the new layers of (digital) ink and colour blend into the image. Taking a step back and leaving it for a few days helps; when I return, I get to tackling the lighting.
Many, many layers and adjustment layers later, we arrive at: