Argyrotype: developing and fixing

[Tony Rye <tony.rye@celandine77.freeserve.co.uk>]

As a newcomer to alt. proc. I have started playing with Argyrotypes and
have subsequently found this list and the archive a source of much
useful info. Argyrotypes may not be the simplest starting point (?) and
I have two intermittent but significant problems. The archives have
provided some useful pointers, but I am still searching for a complete
solution:

1. during development the print can darken considerably - the shadows
fill in and the print contrast is very excessive. I have been trying to
systematically rule out chemical contamination, fogging from daylight,
choice of paper, and side of paper used. Since the image stays on the
paper, and doesn't leach out, I assume this is not a problem with the
paper (e.g. Whatman HP) and must have a chemical origin?

2. during fixing (hypo 1-2%) the print can leach out into the fix,
leading to a massive image loss. The archives suggest: reducing fix
concentration to 1% (may have helped a bit), and gold toning before
fixing (expensive when you are at the bottom of the learning curve),
adding more Tween (or photoflo ?) (may have helped but hit problem 1.)

Have I missed any possible causes/remedies?

Many thanks
Tony