Casein Fixative for Pastel by Spectrafix

Fixatives for pastel continue to be one of the most discussed issues between pastel artists.
The use of casein as a fixative is not new, in fact it is mentioned in the Cennino Cennini's "The Craftsman's Handbook"(Il Libro dell'Arte) from the XV century.
A reference to it can also be found in "The Pastel Artist's Handbook" by Sally Harper.
Recently a new casein based fixative for pastel has been presented by Ms. Natural.
The name of the product is SpectraFix and according to the maker it's colourless, non-yellowing and possesses archival quality.