Re: Opacity of digital negative substrates, was Re: Gum a la Sam Wang

To clarify, I said the following in the previous message, not Judy Seigel.

Judy,

Sam Wang makes a pretty compelling case for the advantages of working
with dry dichromate and I don't frankly see that it is any more or
less dangerous than working with the dichromate in water solution. I
always mix dichromate over the sink and have not observed any powders
or such flying around. However, my purpose in recommending the use of
dry dichromate was only for the purpose of testing the actual impact
on speed and contrast of different strength solutions. It is
difficult for me to see how one could make the test work with diluted
solutions without changing the ratio of water to gum in the mixture.
I grant that it could be done but it would involve some fairly
complicated calculations. Making the test by keeping the amount of
water, gum and pigment constant in the experiment would ensure that
the only variable would be the amount of dichromate.

The main issue as I see it is the one posed by Chris. That is, what
is the minimum amount of dichromate one can use and maintain good
speed and contrast? The answer to that question has implications,
whatever your actual working method.

Sandy King

>On Thu, 27 Nov 2003, Sandy King wrote:
>
>> Judy Seigel wrote:
>>
>> >
>> >> One of the obvious problems in carrying out this kind of test with
>> >> gum is that you would need to be able to weigh accurately extremely
>> >> small amounts of dichromate. For example assuming that you took as
> > >> your norm 10ml of coating solution, to run tests with sensitizers in
>> >> the 1% to 10% range would require that you be able to measure
>> >> accurately from as little as 0.1g to as high as 10.0g.
>> >
>> >To put it mildly. And, as noted, no particular reason to do so. Or none
>> >that I can see.
>>
>>
>> Judy,
>>
>> The reason should be obvious. Protection of *your* environment. The
>> way you work results in pollution of the environment with more
>> dichromate than is necessary for the application. Just do the figures
>> and and show me if I am wrong,
>
>Sandy,
>
>I think we're talking about 2 different things... I'm addressing the use
>of dry dichromate. What seems implicit in your reply is the assumption
>that you use less dichromate if you use it dry -- rather than the same
>amount per print only dissolved in water. Why would this be? I've always
>diluted the dichromate solution well beyond the standard 26% or even 10%,
>hence used less, since I find that coating & developing work better with a
>thinner emulsion. I think probably my present practice remains heavier on
>the dichromate than 1/2 of one percent, tho I haven't checked YOUR math on
>that figure !!! -- but, math aside, perhaps you can explain why suitable
>dilution can't be made up & used accordingly.
>
>Not to mention that in my experience it's next to impossible to measure
>out dry dichromate without having fly-around particles, which would by
>"dry" system occur with every print -- as would of course be more harmful
>to me and my PERSONAL environment than trivial amounts (what isn't
>oxidized or hardened into image) entering the water course, that EPA told
>me was removed anyway in treatment plant. On top of which, as i do mop up
>of work area, and the particles then enter the water stream, I daresay at
>least the same amount total dichromate would be ultimately dispersed, not
>to mention the effect on my IMMEDIATE environment, which could at some
>point remove me from other good works.
>
>Judy
Received on Fri Nov 28 19:09:46 2003