Hi Marc, I hope you figured out what the problem was. I have just gotten back to marbling after not printing for a long while and was releived when it all worked, but am familiar with the mysterious frustration when it doesn't. My theory on the colors looking weak:
1) paints may have settled and most of your pigment load was in the bottom, therefore colors not as concentrated
2) too much time elapsed between aluming papers and marbling them, and/or direct sun on papers before printing, can make the alum less effective
3)temperature and/or humidity--could papers have been less dry?
4)if you were using municipal tap water, the water treatment plant "shocks" the system with chemicals from time to time--perhaps it was a water issue.
Is it possible you forgot how much you need to compress the colors to make them look strong on the paper? If you don't do it as a rule, try putting gall water down first.
For a nearby resource of alum without mail order when you need to get to work right away, try the local garden center or farmer's coop, as aluminum sulfate is sold there as a fertilizer. Dry alum does not go bad but alum in solution definitely weakens. Alum mixed too strong can contaminate the size quickly and cause other problems.
May the marbling muse be with you next time you try it!
--- In Marbling@yahoogroups.com, "sidestreet6862" <bannerworks@...> wrote:
> Hi all. I'm marbling for the first time in two years. I'm doing everything like I've always done -- same paints, same paper, same alum, same procedures. Paints seem fine. However, on the paper, the colors are weak and faded. I can think of no reason for this except the alum.
> I mixed a new batch of alum (double strength) and now have a host of additional problems. The alum I'm using is from Colophon but it is several years old. It's been stored dry in a dry climate. Can it have gone off somehow?
> Also, if I need new alum, will grocery-store alum suffice, as I need it now?
> Many thanks for any help.
> Marc Horovitz