I can't answer directly because I've never taken a
densitometer to a selenium intensified negative. However,
the split toning effect of Selenium depends somewhat on its
dilution. The split tones That result in insufficient
protection come from the use of highly diluted toner (1:20)
but becomes less as a more concentrated solution is used. At
1:9 the effect is small enough to provide good overall image
protection. It is more even at higher concentrations and as
toning is carried toward completion.
   Selenium toner has some advantages as an intensifier: it
is packaged and it is more controllable and reliable than
most other intensifiers, the image is also permanent, not
true of some other intensifiers.
   There are more powerful intensifiers but they tend to be
less predictable. Probably the best of the lot is chromium
intensifier but Selenium is better if it will go far enough.
Silver intensifier is the only one resulting in a neutral
colored image.

I've used selenium toner (KRST at 1+3 dilutions) for approx. 5-12 min. to
many intensify negatives (120, 4x5, 8x10). I don't have a densitometer, so I
have no info on your last paragraph. But it did seem to be easily a grade in
paper improvement. It's been a few years now but I used to do this to
increase contrast in the neg when printing on graded papers. With VC papers
I've not been as motivated to selenium intensify. The density increase
effect seemed to me to be directly proportional to the amount of density in
the original neg.  I found it to be very similar to longer negative
development time - it gave me a second chance. I preferred it to increasing
the paper contrast grade. It worked quite well and it seemed to be
foolproof. I never ruined a negative nor was I ever really disappointed. I
found that reducing dense negatives (overdeveloped) was not nearly as
successful as being conservatively (a little) short in development time and
then intensifying only if required.

Intensification occurs quite slowly often (depends upon film type) with an
increasing plum or blue colour to the neg. It worked well incrementally i.e.
try a little, dry and contact print, then if not enough repeat. I used to do
it by inspection using two large Pyrex dishes with tungsten lights
projecting through the dishes from below. I would visually compare the
difference for negs in a holding bath of water with those being toned. The
lights also kept the temperature of solutions quite warm which reduced the
time and kept the rate of toning consistent. I recommend good ventilation,
warm KRST in theses dilutions is very smelly and somewhat irritating.

Douglas

RE: Frank Earl <fbearl@junkmail.com

   Search this NG for, slimt adams . Ansel used selenium to
gain one zone.                                           Dan