Re: possible answer to archivalness comparison between carbon gum andpt/pd
Shadow values of 2mm above the substrate is awfully high. I have never seen a carbon print with anywhere near that much relief. My own prints, even with my high relief tissue, tend to have no more than about .2mm of shadow relief over the substrate. But even this amount can be rather spectacular on some substrates.It's possible the numbers I'm remembering are the raw heights, including substrate -- I measured the total thickness on a surface plate and subtracted the substrate thickness, twenty-some years ago. Still, I'm sure some of these old prints have at least 1 mm of actual relief. (No wonder they cracked!) I have a few of the negatives they were printed from, and they give new meaning to the term "bulletproof." I haven't measured them, but I've never made negatives with even close to the same highlight density, and I typically make very dense negatives. I'll see if I can find some of the prints and re-measure them in the name of science.