Re: Gum problem(s)

Date: 11/23/05-02:52:07 AM Z
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If PH does affect Gum, then like Cyanotype and other processes, would gum not
work well with a highly buffered paper?

Mark Nelson
Precision Digital Negatives

In a message dated 11/22/05 7:27:43 PM, writes:

> 6. Adding an alkali to the gum/dichromate mix: this changes it from orange>
> to lemon yellow; if so much is added it is converted into a monochromate,
> and the light sensitivity drops to 25%. The higher the pH of the layer, the>
> longer the required exposure. Chromates, thus, are slower than dichromates.>
> With added ammonia, you may start out with a high pH in solution, but due
> to> the volatility of ammonia, it evaporates during drying and the pH of the
> coated layer returns to a lower pH. If a solid alkali is used (sodium
> hydroxide or carbonate) the alkalinity of the dried layer remains the same.>
> The useful life of a sensitizing *solution* is greatly increased with
> addition of ammonia. If pH is 8 or higher, deterioration of solutions is
> practically nonexistent (note: not coated paper).>
Received on Wed Nov 23 02:52:28 2005

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