Is the emulsion truly "on top of the plastic, or is it properly "on top of a layer of Titanium Oxide" - which is desirable for a "bright white" and "uniformly white" background for the emulsion?<<<<
>>>Mylar cored - or PE cored - papers would be even better - the big drawback here is cost. Ilford produces an Ilfocolor "Deluxe" - or something that sounds like that - with a plastic core - I've used it - interesting stuff - it reminds one of a sheet of metal - and I like it a LOT, but it costs something like three times as much as regular (fiber-cored) Ilfocolor - the stuff I use for nearly all of my color printing.[/quote]
BTW-- this is sorta what threw me here in your post--before I spun off into the standard archives rant I seem to be afflicted with--must be poor morale or something.....
PE cored would be polyethylene--not Mylar which is polyester. Polyester is a better plastic, very stable and hard to tear/cut. If you look at film-- alot of roll films are on acetate or some variation of it, and this base can shrink with age actually-- it buckles the emulsion right up off the base. It can lose like 10-15% of it's size as it degrades. The average lifespan for a roll of b&w film in normal conditions is only about 50 yrs or so, but for the polyester based films (mostly sheets), it's much longer because the plastic is more stable. This is why it's used in microfilm...the other worry is then the emulsion--and this is why they use sulfide toners. In a preservation project, they make a "master" copy and then use dupes, or "surrogates". The master is never really used, but kept in a cool/cold vault or other type of room.
But polyethylene is a cheap plastic-- a ciba (classic) was on some sort of solid white melinex base, so the theory was that if a b&w paper were made like this it would have been a sheet of white polyester. I don't think there is such a thing as a PE "cored" paper--in that it's a paper core inside 2 layers of polyethylene. At any rate, the emulsion is on top of all this mess--even if it's the TO that causes problems and worries---the emulsion can still fade, stain and get attacked by pollutants.
Doesn't surprise me that the Ilford paper costs more than regular paper though--we use some Mylar D enclosures and they cost about 3 times as much as polypropylene, and even more than polyethylene--but here again, it comes down to the environment--at a certain point, even these "safe"materials can cause damage--you see that in sleeves & enclosures alot. It all comes down to the temp & rh. I went to an IPI workshop once, and it was a great weeklong learning experience--so packed with info, you just couldn't take it all in. One thing they kept saying was to tone everything. Film, paper, etc. Tone everything in selenium or sulfide toners. The other was that when it came to film, there were 2 priorities--the "needs of the base" and the "needs of the emulsion". The base was controlled by the environment--and if that failed, it wouldn't matter much about the emulsion at that point. I know there are inherent differences in all these materials, and it might seem odd to talk of film & prints lumped together, but silver is silver...
my opinions only, KT