RE: Gum oil
That's neither here nor there -- for all we know Koenig's illustrations were all created in Photoshop. The point is that you bought the book !I purchased the book and still found it lacking but perhaps I wasn't savvy enough to ferret out the salient details of the process, especially the section on digital positives.
Sorry, I wasn't refreshed. Let me say very tactfully, since I believe this post may be public or become public (and I remember that one of my admirers who shall here be nameless sent Koenig my remarks about his book stated on this very same list long long ago) -- I would have liked to like that work more than I did.It was refreshing to see the work at the links posted by Katharine.