How many gum layers (Re: ferri sesquichlorati)
Halvor, I'm coming late here; you've just posted your revisiion, but since I've already written this I'll go ahead and send it:
I agree that how many layers depends on the thickness of the layers (BTW the same gum emulsion goes on thicker on nonabsorbent surfaces than paper IME) and on the substrate (my experience has been that I can print fewer layers on nonabsorbent substrates rather than more, but that may also be partly related to my experience that the layers are thicker on the nonabsorbent substrate).
As to the relief effect Keith described, I think it's also related to the paper you use how many layers it takes to get this effect. With Arches bright white, if I'm printing a fairly high-contrast image (very thick areas of gum interspersed with very thin areas of gum) I get this effect even with one layer of gum. If you look at the print from the back, you see the image in relief in the paper, that's how pronounced the relief effect is. I thought at first it was a differential shrinking of the paper around the gum and assumed I could avoid the effect by preshrinking the paper, which I don't ordinarily do, but found to my surprise that preshrunk paper does the same thing; it's apparently a relief thing not a shrinking thing that's going on.
By the way, a couple of years ago I took one of these warped prints and had it dry-mounted to flatten it, and announced that solution here, but I don't think I'd do that to a finished print again, because it seems like it would mash down the relief. People seem to be fine about the relief effect, in fact they like it, so I've decided not to worry about it. Like I said, it's only noticeable with a print that's fairly high contrast.
On Oct 23, 2006, at 6:24 AM, Halvor Bjørngård wrote:
Hi Keith :-)