Re: Gum problem(s)

> I kind of decided at this time to use only a 21 step tablet to acquire an
> intuitive feel of the various parameters involved and how they affect the
> results. Also, I'm not expecting the top most 10-11 steps to print any
> thing
> else then "pure" white. As for the 20 minutes well I would argue that it
> depends a lot on your light source, the composition of its light and the
> minimum and maximum optical density of the negative you're using be it
> digital or whatever else. In my situation I could argue that I could use a
> bit more time because I can see a tiny difference from step 1 to step 2
> and
> I assume overexposure would start to happen when these lower steps begin
> to
> look all the same, yes/no???

Of course exposure depends on your light source--if I were to still use the
sun, if I remember the exposures were 30 seconds to a couple minutes. Now
under UVBL it is 6.

What I have decided with test strips and gum is, since you're hardening a
deeper and deeper layer of pigmented gum, sometimes you just have to choose
a time that gives a stable coating and go with it. In other words, if you
expose a print at 20 minutes and get a nice deep layer of color in the
shadows and still have highlights that clear, then 20 minutes is perfect.
If you expose at 6 minutes and your image washes away, then you know you've
underexposed. I can expose at a range of, let's say, 10 to 4 minutes, and
yet I've chosen 6 because I get a deeper layer of color with 6 than with 4,
coupled with a normal development time of between 1/2 hour and 1 hour (less
if sprayed) and with spray development the layer is quite stable. It works
for me, under UVBL with diginegs, but your light source is way different and
I wouldn't begin to suppose I could extrapolate a time for your light
source.

>> BTW, the idea that the dichromate may, in fact, expose the layer at the
>> bottom (I wouldn't have a clue if it did or not) probably stems from the
>> observation that when you first soak your paper in the water face up, all
>> the dichromate leaches out immediately. This only takes about a minute
>> to
>> happen, and then you can lift the print out of the water and watch the
>> dichromate stream off. The layer is still perfectly intact. I have no
> idea
>> chemically why this is so--the chemists of the list can answer that
> one--but
>> I have observed sometimes in coating a paper with magenta that in my
>> brush
>> strokes the yellow of the dichromate brushes at the paper base and the
>> pigment seems to be on top, so perhaps the dichromate is of a different
>> weight or whatever the term is chemists use...mole...blah blah..
>>
>
> As I've writen elsewhere I have a big, very big problem with this theory.
> At
> this time I don't see how it's even remotely possible but I could be dead
> wrong on this.

You're not--I'm just explaining why the theory might have been suggested in
the first place because the observation not based on science seems like
that.

Size that paper.
Chris
Received on Fri Nov 18 12:20:35 2005