[Fwd: Wet & Dry Exposure]


Jeffrey D. Mathias (jeffrey.d.mathias@worldnet.att.net)
Fri, 30 Jul 1999 18:13:59 -0400


 Eric Neilsen wrote:
> >
> > Jeffrey, How long do you wait in between coating and exposure? for wet or dry?
> > My point being that if you don't wait long enough or get it dry enough, the
> > paper will have more and maybe quite a bit more humidity.
 
 I will try to answer a bit more precisely. Although the best thing
 would be for you to come visit and observe what I am doing. If the
 paper is going to hold the humidity that well, then it's probably going
 to hold it away from the coating on the surface as well. I suspect
that
 the RH of the coating is responding to a controlled value reproducibly
 even though that value is not known.
 
> > ...
> > With steam or a sonic mister, in a controlled environment such as a enclosed
> > box?...
 
 Humidified with a sonic mister, no enclosed box. I just let the paper
 soak up the moisture from the mist (without any droplets forming or any
 spray hitting the paper) until it feels "right" "limp" "not crispy".
 This feel is about the same every time, but may differ with various
 papers. I also mist both sides, one then the other several times. It
 usually takes a couple minutes, more in drier climates, less in wet,
and
 depends on how the paper is stored, but I do not time, I feel. (One of
 the reasons to not use steam is that papers phisically coat better when
 cooler.)
 
> > If it is consistent and repeatable that is good, but how long do you dry it?
> > did that change from Tucson, to Tampa, to New England? solely by feel?
 
 Again by feel. However when I started POP this spring I started noting
 of how long it would typically take. This seemed to be about three
 minutes whether by the "wet" method or by the "dry" method. Sometimes
 the "dry" takes longer as I don't want to use too much heat. The "wet"
 has been check by rubbing my finger lightly across the coating to
 evaluate how rough or smooth. Both sides are blow dried several times.
 
> > It would provide more information if "wet" was qualified with an measured RH.
> > Perhaps 75% is too wet and allows the solarized areas, whereas 65% would not.
 
 Again I do not have the equipment to measure the RH of coatings or
 paper. I you do, bring it with you when you come and we'll try to get
 some numbers. It would be nice if the solarization effect stops at
some
 lower RH. Remember I only called this a preliminary test for "wet" and
 "dry". It seems some in-between data would be in order. I do plan to
 repeat the "wet" exposures at ambient RH set to 60% and 55%. BUT, IF
 the massive high contrast printout is lost, I believe so will any
 advantage of exposing "wet".
 
> > And as Tony mentioned, it is easy to make a Ziatype, but difficult to be
> > consistent. This is why knowing the RH of the wet state would be very
> > valuable. You have produced some very valuable information concerning the
> > concentration of solutions used in the ammonium based system of platinum
> > printing (POP), I find it hard to understand how the concentration of water is
> > being seemingly , dismissed by you.
 
 AGAIN, I HAVE NO EQUIPMENT TO MEASURE IT. Further I am convinced and
 satisfied that the RH is being consistently controled. The work I did
 with optimizing solutions for POP was accuratly repeatable at all of
the
 ambient RH at which I made prints. These ranged from 45, 50, 55, 60,
 65, 70, 75, 80 % according to my ambient RH meter. I found
difficulties
 and problems over 65%RH which were experienced by others on the list
who
 limit there RH to 60 to 65% maximum. I would get identical results in
 prints when setting the room at a certain ambient. All the time my
 processing technique remains the same. I feel these to be a good
 indicator that my RH zones are in the right ballpark.
 
> > Others may disagree with me, but its the
> > water content that is enabling the print out, and must be considered an
> > important component that needs controls.
 
 But, this is one of the things I noticed as well. With the only
 difference being RH, the "wet" one had a very dark, black, very high
 contrast printout. It is important. The question is how much control.
 The more important question is can the "wet" technique be controlled to
 not produce the solarization effect and still keep the dramatic high
 contrast printout???

-- 
Jeffrey D. Mathias
http://home.att.net/~jeffrey.d.mathias/



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