From: Jeffrey D. Mathias (jeffrey.d.mathias@worldnet.att.net)
Date: 02/06/00-04:36:41 PM Z
Philippe Ayral wrote:
>
> My question is about quantity to use.
> Let's say I did a test with 4 drops afo, 4 drops LiPd and 1 drop of Ammonium
> dichromate 2%.
> I like the test and my final print will be double size than the test.
> So, I will use 8 drops of afo, 8 drops of LiPd but I don't know if I must use
> 1 or 2 drops od Ammonium dichromate 2% to get the same result.
> ...
Like Carl answered, I would also recommend 1 drop of a 4% solution.
However consider the following. The two drops of 2% into a total of 10
drops will have a strength of 0.4 % AD. One drop of 4% into a total of
9 drops will have a strength of 0.444 % AD. This 10% or so difference
in the contrast agent will hardly make any noticeable distinction in the
prints. A 50% difference can make a minute change and typically the
contrast agent is doubled or halved (100% difference) to provide a
change in contrast.
A very important factor to keep in mind is that the area coated is
critical for the amount of metal and sensitizer chosen. If additional
water or contrast agent is added, the total mixture must be coated into
an identical sized area or the resulting print will be different. Also
the final (double the chemistry) must be coated into double the area.
Brush marks out side the area are decorative and must have additional
coating mixture to accommodate them. The carefulness or necessity to
stay within an area becomes less of a concern or even a moot point if
the threshold of the coating material is exceeded for the given paper
and coating technique. This is a reason why knowledge of the threshold
can be an important tool in understanding and controlling the process.
-- Jeffrey D. Mathias http://home.att.net/~jeffrey.d.mathias/
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