Sandy King (sanking@hubcap.clemson.edu)
Mon, 15 Mar 1999 22:11:20 -0400
I nearly always work with replenished dichromate with carbon printing and
have done enough testing to know that it works. I would not presume to say
whether this would work with pt. However, in carbon the actual amount of
dichromate needed to sensitize a tissue is so small that it seems like
something of a crime to mix a large amount of solution and discard it after
one use. And of course, if you don't replenish the solution, the printing
qualities of the sensitizer will change gradually over time in such a way
that you loose control of the sensitometry of the process.
I work with a liter of sensitizer for tissues up to 12X20. After
sensitizing I filter the solution back into the bottle and add back enough
dichromate of the same % to top it off, then store in a refrigerator. I mix
all dichromate solutions with distilled water and run frequent tests to
make sure that the pH does not change. Right now I am working with several
bottles of sensitizer that were mixed over three years ago and their
printing quality is virtually identical to when mixed fresh. And of course,
the beauty of this working procedure is that you are being very kind to the
environment with the small amount of chemistry being used.
The only exception is when working with negatives of low contrast that
require a very dilute sensitizer ( on the order of 1/4 or 1/2%). The amount
of dichromate needed to make a working solution is so small in these cases
that it hardly makes any sense to worry about replenishment so I mix fresh
solution every time and discard it after use.
Sandy King
>>>Has anyone had this problem or explored replenishing the
>>>dichromate? Does it wear out? Thanks.
>
>
>
>I have never replenished this type of material. I prefer to mix it fresh.
>The problem I have with any form of replenishment is in how replenishers
>for developers work. A common problem some people make is in simply adding
>more stock solution to exhausted developers.
>
>This is not replenishment in that replenishers are specifically designed
>for specific developers. DK-50 developer is one I constantly replenished in
>a deep tank dip and dunk line. I also used deep tanks and Ethol, which was
>replenished with Ethol Replenisher as volume was lost.
>
>I also think that some materials, if 'replenished' by simply adding
>additional fresh chemicals to bring up the volume leads to inconsistent
>results. I think you would require an altogether different material if you
>were interested in true replenishment.
>
>RM
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