people often miss stuff that's right under their noses - by the shadow effect. It's important to bring stuff into popular consciousness - this is how we were ...
I've not seen anything even slightly resembling a Celtic Head figure in either of Stan's two books that I've read. When I first rang him up we spent the first ten minutes arguing the meaning of 'pepperbox patterning'. (All the pepperpots I've seen have a regular pattern of holes).
Maybe it would be useful to have a clear image of the panel - I don't know how that would be done - sheets of brown paper, held by masking tape, and a soft wax crayon? And then photograph that image against a flat well-lit surface ?