Correction
Second question first. Do NOT split fixing time. A print is
to be entirely fixed in the first fix. The capacity of the first
fix can be VERY high. Dissolved silver levels in the first fix can
be very high. There in lies the reason for the second fix.
Only that portion of the first fix which is carried by the
print enters into the second fix. The great bulk of dissolved
silver remains in the first fix. A second fix reduces considerably
the levels of dissolved silver and residual silver in the emulsion
and paper. The name of the game is, reduce dissolved silver
to a very low level.
BTW, The Compact Photo Lab Index quotation is speaking
of the slower Sodium Thiosulfate fixer. Two hundred 8x10s
is a lot of prints. The chemistry's capacity though is even
greater than that with film or RC print procesing. With
those two higher silver levels are OK. Dan
First paragraph second sentence: Do NOT split fixing
time. In context that sentence makes no sense. In reality
we are talking about a two bath fix. Some time in each.
A 50-50 split of time MAY be as workable a division
as any. Probably somewhat arbitrary.
Off hand though I think a 2/3 - 1/3 split might be better.
As the first fix loads with silver and it's halide components,
chloride, bromide, and some times iodide, it becomes slower.
The second fix which is to become first fix is to be kept
quite clear of silver and those components.
The thiosulfate ion has a great affinity for silver. Literaly
the silver is yanked from it's halide components. Essentialy
a matter of so much silver, so much thiosulfate; a quantitative
relationship be it chloride, bromide, or iodide. The three
being less and less soluble in that order.
The concentration of the fixer has nothing to do with
a complete clearing of the silver. Years ago I used to think
there was some magic level of strength below which a fixer
would not work. Now days I use fixer very dilute, one-shot,
with archival results from one bath. No stop needed. Dan