I was in Chicago early this week and made my usual stop at the
Art Institute. While looking at the current exhibit from the permanent collection I noticed that a couple of the Irving Penn platinum prints said they were mounted on aluminum plate. Can anyone explain why this was done? Archival purposes or simply something to do with the original presentation by Penn?
While I can't know for sure the reasoning behind mounting on aluminum, it certainly would be archival beyond any acid free mount board. Provided, of course, that the aluminum was properly prepared. Aside from that it represents an absolutely flat surface. Additionally aesthetic considerations may have entered into the decision as well. There may be other considerations of which I am not aware.
Dan Burkholder in his book on digital negatives says that he heard "from a reliable source" that the reason they were mounted on aluminum is that Penn coated, printed and developed his platinum omages multiple times, with different contrast sensitizers for each layer. The reasoning behind this, I suppose, would be to use a low contrast sensitizer to print the nice delicate highlights, then follow with a high contrast sensitizer to give the shadow areas some punch and additional contrast. The aluminum substrate was to ensure that there would be minimal shrinkage between printing and drying cycles. He was in effect doing something similar to split filter printing with VC paper.
This is more or less the process I use when I do my gum-over-platinum prints, with the additional benefit of being able to choose pretty much any print tone I want. I think aluminum might be a little overkill. I just pre-shrink my paper before I do my first platinum layer, and I have very few problems getting the gum coat (or coats) to register properly. Multi-coat gum printers have been dealing with the problem of substrate shrinkage for over a 100 years and it really is not that hard to handle.