Re: lemon juice and gum printing

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From: Christina Z. Anderson (zphoto@montana.net)
Date: 06/30/03-10:51:26 AM Z


P.S. Ohhh, Sandy; I just thought of a variable I am forgetting, after you
mentioned below the three at the same strength, and this is why I MUST
retest it like that: sodium dichromate is thick and syrupy and brilliant
deep yellow at full strength; is it possible I am getting a faster speed
read on am di by virtue of sodium's greater density?? When all three are
painted side by side, pot is a thinner yellow, am is deeper yet, and sodium
the deepest, and also, I assume, the thickest as it is more viscous than the
am di solution. Could that really hold back a full stop (and maybe 1 1/2) of
exposure?
     I need to find my packed Kosar.
Chris
----- Original Message -----
From: "Sandy King" <sanking@clemson.edu>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Sunday, June 29, 2003 11:10 PM
Subject: Re: lemon juice and gum printing

> Chris,
> > What I don't know and maybe you can answer is this: do two steps
on
> >the 21 step wedge equate to a stop? If so I would say am di is faster by
> >about a stop to a stop and a half.
> Two steps equal about log 0.30 density, which is indeed about a stop.
> However, I think you are confusing speed and contrast. The speed of a
> photographic emulsion is generally considered to be the point on the
> step wedge where you have the first maximum density in the shadows.
> Contrast is determined by how many visible steps you have. Less means
> a printing exposure scale of greater contrast, more means less
> contrast.
> In your tests what you have found is that ammonium dichromate gives
> less contrast, or softer results, than the other dichromate. This is
> true even when the dichromates are compared at the same strength
> solution.
> Sandy King


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