Under UV light, this painting appears black and grey, without emitting the least luminescence, so it is very difficult to find it with the Wood lamp, whose use seems restricted to red no. 4:
• Dots and red fingermarks seem restricted to this paint.
• It is never on flaked surfaces, unlike paint no. 4.
It should be possible to confirm the distinction between the two paints, and this is suggested by preliminary tests carried out with a scanning electron microscope (Eric Beucher 'Analyses & Surface', Louviers, Eure).
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