RE: pt/pd mounting
The following is copied from Mike Ware's page at http://www.mikeware.co.uk/mikeware/Eighth_Metal.html. Hope he won't mind if he finds out... Liam The third attribute -of permanence- had been a longstanding issue ever since the Fading Committee of the Photographic Society reported in 1855, and the Duc de Luynes' prize for a permanent process was won by Poitevin (for Carbon printing) in 1859. Willis's platinum research was also stimulated by the quest for permanence, but even after he had finalised his procedures, we find many articles in the photographic literature complaining of incomplete clearing, and offering suggestions for curing yellowed highlights in Platinotypes. A modern investigation of this problem, and the extent to which it can be attributed to residual iron, has recently been carried out by Rees and Gent at the Victoria & Albert Museum (48). Although the metal constituting a Platinotype image is invulnerable, its paper substrate is certainly not. Acid embrittlement of the cellulose is the other besetting problem that Platinotypes present to the conservator. The build-up of acid is exacerbated by the catalytic action of the platinum black itself, which assists the conversion of sulphur dioxide to sulphur trioxide and hence to sulphuric acid (49).
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