<< But that's not why I'm writing -- I'm writing about Crawford. Since when
is Crawford the *authority* for gum printing? >>
:)
I have a suspicion that he probably had some misunderstanding about percent
solution as well. I hold nothing against him or his book, and like Judy, I
have read his books several times. I don't have the book in fron t of me right
now, but the numbers that Sam quoted:
<< In his Keepers of Light, William Crawford said to use 35.7 grams of
ammonium dichromate in 64.3 ml of water for making the sensitizer. >>
Notice that the numbers are nice (35.7 + 64.3 = 100). My guess is he must have
read from some chemistry or material sources that say the ammonium dichromate
saturates at 35.7, thus he is suggesting making a saturated solution, but in
general adding 35.7g somthing to 64.3 ml of water does NOT make a 35.7%
solution. Maybe it just so happens w/ ammonium dichromate although I doubt it.
But if he indeeding meant 35.7% or saturated solution, then Sam's question
still remains: why are people using so much amount of dichromate when there
doesn't seem to be any difference.
Incidentally, the recent discussions show something that I have mentioned in
the near past: that contradictory evidences or experiences certainly do not
mean one of them is wrong. Sam says that changing the proportion of dichromate
in the final mix does not give much different (if at all). Hamish says that
changing the proportion DOES. *Both* are true evidences. It's just that the
are using the same terms to describe slightly different things because again,
the "variable" is not *just* the proportion of the dichromate but the
proportion of it and the proportion of gum and the proportion of water and the
proportion of pure pigment and the proportion of gum from the watercolor
tubes.
Dave S