From: Katharine Thayer (kthayer@pacifier.com)
Date: 07/05/03-05:15:53 AM Z
Sandy King wrote:
>
>
>
> With carbon you can get the same results with either ammonium
> dichromate or potassium dichromate, so long as you adjust the amount
> to account for the greater sensitivity of ammonium dichromate. I find
> that a 3% solution of ammonium dichromate will give almost the same
> results in terms of speed point and number of printable steps as a
> 4.5% solution of potassium dichromate.
>
This observation is consistent with what I've read in the literature,
that in order for the two dichromates to perform similarly, the ammonium
has to be mixed at a lower concentration than the potassium, 70-85% of
the concentration of the potassium dichromate; it is also consistent
with my contention that the differences in properties of the dichromates
aren't purely a function of dilution.
This equivalence works only up to the saturation concentration of
potassium dichromate, as I've said elsewhere. Since gum printing uses
higher concentrations of dichromates than carbon, the differences
between the dichromates become more important for us.
kt
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