>Recently I started trying to size paper (BFK) at home with the chrome
>alum/gelatine mixture outlined in the archives. My previous experience with
>gum printing has been on formaldehyde hardened paper in a school setting.
>
>After 4 exposures I noticed that the gum/pigment seemed to be sloughing off
>in various areas of the image giving a slightly mottled look.
>SNIP<
My "hand made papermaking" sources tell me that chrome alum sizing is now
considered non-archival (it shortens the life of the paper). I think most
gum printers (those actually using gum arabic, as opposed to gloy or
various glues) are now using Glyoxal.
This is available from a few fully stocked chemical houses, or from the
list's own Richard Sullivan. It is still a chemical to be careful with,
but seems (from list comments and the unscientific test of: I now get less
headaches) far safer than formaldehyde. Richard, and a few others on the
list, will suggest using 25ml per liter of water at room temp for about ten
minutes. I found I got less staining using 15ml per liter. Glyoxal seems
to have a bell curve, too little and you get staining, too much and you get
staining. This may have to do with both paper and gelatin choices.
Your image "sloughing off" may be too much pigment or too hot wash water,
as opposed to incorrect hardening. With the paper/gel/hardener I typically
use (Lana HP, Tri-Ess hard gum, glyoxol) the gum/glyoxal is simply to
minimize the staining.
tomf2468@pipeline.com (Tom Ferguson)