I'm a newbie to making leather bindings with paste. The problem I'm having is a staining of the leather, apparently by the absorbed paste.
I'm using veg.-tanned, aniline-dyed Packer Leather bookbinding kangaroo, whisky (tan) color, .6 mm. I'm moistening the hair side with distilled water until the moisture starts to show through on the flesh side, then I paste the flesh side, wait for absorption, repaste, and apply the leather to the boards. I'm using Talas pre-cooked wheat paste and Lineco acid-free boards.
The work dries with dark patches. The overlap of the thinned edge fold-over is particularly dark.
I've tested the leather itself, and it will take a total wetting and drying cycle with no discoloration whatever. Add the paste and the stains appear on drying.