Two views of the creation of the Arnolfini portrait

I think it helps to bring together a range of evidence to see general trends and distinguish explanations. From my analysis, for the Arnolfini portrait we must choose between two mutualy exclusive cases:

CASE 1:

• that nearly a century before any record of how such a concave mirror might be ground (in a personal notebook of Leonardo's, in a different language, with obscure handwriting, over 1000 miles away)
• that in the absence of modern demonstrations of hand-creation of a long-focal length concave mirror by blown (and possibly spun) glass that could be silvered to produce an adequate image
• that in the absence for millennia before and centuries later of any corroborating evidence that a long-focal-length concave mirror even existed , despite numerous parties who had every reason to disseminate such information, in light of evidence for other mirrors that could not be used for projecting images implied by every painting so analyzed
• that in the absence of any corroborating evidence that anyone in 15th-century Europe had even seen an image projected by a concave mirror
• that in the absence of any convincing suggestion as to who made such a concave mirror or distributed it
• that in the absence of modern "re-enactments" faithful to the constraints of 15th-century technology leading to a full painted image rather than a mere tracing (see below)
• that van Eyck obtained a long-focal length concave mirror
• that despite the absence of records for books teaching the complicated method he discovered how to use such a mirror
• that two curved mirrors were in Arnolfini's room at the same time
• that in the diffuse skylight van Eyck could adequately see the projected image
• that for some reason van Eyck made a detailed representation of the convex mirror and its reflections including figures in the "old-fashioned" stance for painting (without showing a tent, concave mirror, and so on that Hockney suggests was in fact used)
• that neither Arnolfini nor his wife (nor of course van Eyck) left records remarking on the difference between the way the painting was executed (with mirror, dark tent, etc.) and what actually appears in their painting
• that much important work on the painting was done when it was upside down, despite the fact that the only brush strokes visible in the painting are "downward" (and hence made when the painting was rightside up)
• that van Eyck used a trick suggested, as far as we know, not by any artist in the last 600 years, but by a 21st-century Ph.D. in optics, to paint the Arnolfini portrait using a modicum of drawing ability

CASE 2:

• that van Eyck -- "the father of oil painting" -- exploited the new medium and his own patient talent to paint Arnolfini by traditional methods.