Marion & Co. 1885 Advert for "Marion's Ferro-Prussiate Process."
Advert Internet - Original source ill-defined Source rquested. Published in: Mike Ware, May 2007, "Siderotypes by Sir John Herschel from Steel Engraving Diaphanes," Conference: Literature and Photography: New Perspectives,At: School of Art History, University of St. Andrews, Scotland
