Adapting Technique- Working on Drafting Film

I have been asked several times how I work on drafting film, and is it different to working on paper/board. So I thought it might be useful to do a blog post on the subject.

This Cheetah is approximately 10 x 8 inches, coloured pencil and acrylic on drafting film.

Right from the first marks I work differently on drafting film because it doesn't take many layers. This makes colour selection much more important than when I work on paper. Because I work in very light layers on paper I can correct colours as I go. On drafting film every layer has to count.
I also work on both the front and the back of drafting film, punching up highlights, and darkening lowlights. This gives extra scope for modifying the final colour.
My strokes are also different in some ways as I tend to work quickly establishing a base and then add the detail in acrylic. You can see the acrylic strokes on the cheetah, particularly round the eye. On paper all the layers are worked in small strokes to allow for the optical mixing of the colours.
On this image the background is all coloured pencil applied to both the back and the front. I have not applied solvent just layered the pencil with a very heavy hand, in real life there is a subtle change from black to brown. I will try to get a more accurate scan to show the true colours.
Sometimes I airbrush acrylic if I want either a more subtle or detailed background.