The composition and textures are awe-inspiring.
The frontal images were monochrome but If the images were reversed and viewed from the back, some of the figures would appear in color.
That's because a gel containing watercolor tints was sandwiched inside and covered with tissue to disguise the technique.
The Diableries bear a resemblance to Mexican folk art dioramas (above). Is that a coincidence? Mexico and France were briefly joined (well, sort of) in the 19th Century. Maybe some kind of cultural pollination occurred during that time.
Many thanks to Brian May and his colleagues for what appears to be a terrific book on the subject!