Judy,
When I was actively gum printing I used 14 Ba gum arabic solution prepared
for lithography also. The only reason I even researched gum arabic and
the multitude of other gums was a thought process that the Fresson process
may have required another type of gum.
When you read over those handbooks you'll see that there are quite a few
alternate gum types. However, the major gum types (in addition to arabic)
are Guar Gum, Gum Ghatti, Gum Karaya, Gum Tragacanth, Tamarind Gum, and
Xanthan Gum. In the coarse of testing and researching I spoke with a
technical expert on gums (I chewed the fat with him . . . sorry I couldn't
help myself) who basically said that none of the other gums even come
close to the unique properties of arabic. He also indicated that the
synthetic gums products leave a lot to be desired but they were developed
when the supply of arabic became restricted for whatever the reason. I
have tested a synthetic lithographic gum arabic which worked very nicely.
The synthetic gum arabic I tested was 'EGGEN Agum O' (German made by
Hanns Eggen - Sarstedt) sells for about $20/liter or about 4 times the
cost of natural gum arabic.
I have settled in on using natural gum arabic purchased from a printer's
supply house. I seem to have very repeatable results but my formulations
rely on a mixture of gum and gelatin. The process is quite different from
standard gum printing.
As to your slow gum, I can only guess that the natural variation in gum
arabic based upon geographic location, species variation in the acadia
trees as well as seasonal variation all play into what you are
experiencing. It maybe worth your while to talk to a few importers and
ask to speak to their technical representatives, it may give you some
insight if not an exact answer.
I know this note falls into the middle of subsequent notes on the subject.
I think there is a lot more science or fact known about gum arabic than
most people care to read.
Sincerely, Art
Art Chakalis
Columbus, Ohio, USA