Fleischmann is still regularly acknowledged as author of the most detailed study of Robespierre death masks, but frustratingly his little monograph is unobtainable, apart from a few snippets on Google Books. Apparently he was a sceptic: "Many death masks of Robespierre exist, all false, reconstituted after the fact from portraits", summarises Antoine de Baecque, (p.167).
It is surprisingly difficult to pin down what Robespierre "death masks" actually existed. Vivant Denon once owned one. The only two examples documented on the internet are in the Hutton Collection and a bronze in the Musée Carnavalet, both copies from Madame Tussaud's original mould. There is no clear provenance accessible in either case.
Hector Fleischmann, Behind the scenes in the Terror (1914), plate.p.128. http://archive.org/stream/
_______, Le masque mortuaire de Robespierre. Documents nouveaux pour servir d’intelligence et de conclusion à une polémique historique..., Paris, E. Leroux (1911) 26 p.
Hutton collection: Death mask, from the original in Tussaud Gallery, London.
Portraits in plaster from the collection of Laurence Hutton (1894) p.75
Antoine de Baecque, Glory and terror : seven deaths under the French Revolution (2001)[Relevant passages are available in the preview on Amazon or Google Books].Reproduction of the Carnavalet head , p.144.
See also the discussion: http://revolution-fr.livejournal.com/53118.html