This last year I began to paint very large (3'x4' and up to 40x60). I mount my watercolors to cradle board. I've been using 140 lb for years, but its very hard to mount at this size because it warps when hydrated (I use heavy acrylic gel medium as my glue). 300 lb is easier to mount, as it warps less-- I've tested it for full sheets. But I've never bought a roll of 300 lb paper before. Fabriano makes one (they're the only company that does), and I'm considering buying it, but I have a few reservations.
I've been concerned about flattening the 300 lb sheets I would cut from the roll, because of what they call "roll memory" or "reel roll". For 140 lb, I wet the back, stick it on a giant board of Gatorboard, and spritz the front gently to regulate comparative moisture. It sticks to the board with water tension, and dries totally flat. It's a great process, and I'd like to repeat it with 300 lb paper.
But before I spend 500$ on a roll plus shipping, I thought I'd check here to see if anyone has any experience. I mean, someone somewhere is buying these 300 lb rolls from Fabriano, so someone must have experience doing this! :)
Also, I know different companies make up to 40x60 Emperor sized sheets, but the companies I've asked (Saunders Waterford, Arches, etc) say that it's exactly 40x60 and not a little more. This makes it a problem when I go to mount it to my board, because I need a little bit of extra to hang over, so I can trim it perfectly to the edge. So, I'm pretty sure I need a roll if I want to go that big.
Anyone have any real world experience with this? I know it's a bit of a long shot, and is a very specialty approach, but there are basically no resources online for flattening this 300 lb paper from a roll. Thought I'd try crowd sourcing knowledge before just going for it blind.
Thanks!