Re: Confusing Speed and Sensitivity, (was Potassium vs. Ammonium Dichromate), (was Re: Clearing Gum Prints)

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From: Katharine Thayer (kthayer@pacifier.com)
Date: 03/29/01-09:20:48 AM Z


I think it's probably best not to try to compare differing results of
ammonium and potassion dichromate across different printing processes.
In gum printing, my experience is that ammonium dichromate is FASTER,
meaning shorter exposure times. In fact, I suspect that the reported
observation of some that they get a heavy green-brown dichromate "stain"
with ammonium dichromate is because they don't reduce the exposure time
enough, relative to their exposure time with potassium dichromate.
Katharine Thayer

 
Sandy King wrote:
>

>
> Also, I believe some gum printers (Dave Rose at the start of this thread)
> are using the term "faster" in comparing differences between ammonium and
> potassium dichromate (or in comparing different strenghs of these
> chemicals), when in fact what they are describing is sensitivity. In my
> work with carbon the speed of tissue (as determined by how long it takes to
> print the first maximum black) is very similar regardless of which
> bichromate I use. However, sensitivity is slightly greater with ammonium
> dichromate than potassium, and of course increases significantly with
> stronger sensitizers, the practical range going from about 1/2% up to 6-8%.
> Sensitivy controls how many steps of the step wedge you can print,
> measuring from the first maximum black to the last visible step, and is
> there related to contrast.
>
> Sandy King


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