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Joe Lipka

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Joined
Sep 24, 2002
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908
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It's so tough to make technical stuff exciting...

My last kvetching post was about my inability to get beyond a Dmax of 1.3 when making a palladium print. You provided some good questions, tips and it got me to thinking about what does affect the Dmax. Testing seems to be the solution. I took some time yesterday and came up with some tests to find the source of the problem. Here is what I did.

The test negative was printed on Pictorico Premium OHP. It was a Step Wedge of 2% intervals with the blocking color determined from the last test session. I cut the transparency so the step wedge was close to the edge. I did this so the area covered by the negative and the area without the negative were close together.

I double coated a sheet of Weston Diploma Parchment with 18 drops FO, 18 drops Pd and 4 drops of Na2 using the Richeson 9010 brush. This was an 8x10 area on 11 x 14 paper. I coated the smoother side of the paper. The paper was allowed to dry to a satiny finish between coats. I let it dry a little bit longer after the second coat. I tore the paper into quarters using a plastic straight edge.

Exposure was for six minutes under eight F15T8BL tubes.

Here is the series of tests I ran.

1. Nothing between the light source and the paper.
2. OHP with step wedge between light source and paper.

3. Paper under vacuum frame glass and no vacuum.
4. Paper under vacuum frame glass with step wedge and no vacuum.

5. Paper under vacuum frame glass backed with Saran wrap and 25" vacuum.
6. Step Wedge on paper under vacuum frame glass backed with Saran wrap and 25" vacuum.

All the exposures were made consecutively, all the test strips were processed together with FO developer (108F), rinsed for two minutes, cleared in two fixing baths for 5 minutes each.

Tests 1 and 2 show the effect only of OHP on the final print.
Tests 3 and 4 show the effect of glass and OHP on the final print
Tests 5 and 6 show the effect of glass, OHP and use of a vapor barrier to keep the paper humid during exposure.

The Results (drum roll, please...)

Test # -- Paper Reading -- Dmax
1 -- .10 -- 1.40
2 -- .10 -- 1.10
3 -- .10 -- 1.30
4 -- .10 -- 1.13
5 -- .10 -- 1.15
6 -- .10 -- 1.18

There is a significant drop off in density from the uncovered paper to the paper under OHP, glass and under a vacuum. It would appear that the Saran wrap (I had that at home, not mylar) does protect the humidity of the paper because there is little difference between the OHP and non OHP sections of the test strip. OHP looks to be a major villain in robbing density from the step wedges.

I haven't fully interpreted these numbers yet, but this is just one data point to look at. The initial density of 1.4 is a concern, but that just might be the result of some poor coating on my part. This is a hand process and there can be variation.

Your opinions are welcome.
 
Last edited by a moderator:

Ben Altman

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Joined
Jan 19, 2007
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205
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Ithaca, NY a
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Hi Joe,

Good idea to do some research. Thanks for sharing.

Coupla methodology questions:

- Is your exposure an over-exposure? In other words, are you getting the darkest two steps on your wedge to blend? Otherwise you may be measuring exposure differences due to the various stuff in the light path, rather than some other effect.
- Without vacuum, how is the Pictorico kept in contact with the paper? My observation is that if there is any separation between the two, the negative scatters light around, and that can mess up your DMax. (Particularly with the diffuse light from tubes.)

Best, Ben
 
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