Type 55 works very well for alternative processes, and I use it all the
time for pt/pd, cyanotype, Ziatype, POP and gum.
The 50 ASA rating is for the print not the negative. You have to expose
for one or the other, not both at the same time. I find an ASA of around
12 works best for the negative, but depending upon the final process, I
may have to intensify the negatives in selenium for optimum density
range.
My method is the old Ansel Adams stand-by of one part rapid selenium
toner to two parts tap water (with hypo clear); room temp, agitate 2-5
minutes with constant agitation. The intensification effect is spent at
about five minutes, so further toning is unnecessary. You'll get
beautifully dense highlights with a lovely deep blue cast.
Note too, that trying to save an overall very thin negative is pointless
with selenium as it responds proportionately to the amount of silver
already in the film. Consequently, highlights respond with the most
intensification, mid tones somewhat, and shadows little if at all. There
has to be silver there in the first place. You can expect a full contrast
grade--or even more--increase with this method. Store the unused solution
for future negs.
Hope this helps.
John
John Barnier
12560 Morris Trail North
Marine on St. Croix, Minnesota 55047
USA
jb@dgi.net