Azo - Negative densities

[Donald Miller]

For those who may be interested Jim Shanesy has been kind enough to send me two of his Azo prints and the corresponding camera negatives in order that I might read the print reflection densities and corresponding negative densities with my Xrite 310 TR densitometer. I have posted those images today in the technical gallery on Apug.org. I have identified the points at which the dmin, dmax and corresponding negative densities were read. The negative densities were read on the blue channel to account more closely to the actual pyro stain/silver density.

Additionally, I have recently conducted step tablet tests of grade two and three Azo and read the reflection density of the corresponding steps. You may email me if any are interested in having the results of that testing.

[Michael S. Briggs]

To make it easier, the photos are http://www.apug.org/site/main/album_page.php?pic_id=719
and http://www.apug.org/site/main/album_page.php?pic_id=720.





Print 719 was made on Azo grade 3 using a water bath -- the negative has a
density range of 1.25. Print 720 was made on Azo grade 2 -- the negative for
720 has a density range of 1.38. The details are summarized below:





<table>
<caption>Densities for photo 719, Azo grade 3 (water bath)</caption>
<tr><th>Print</th><th>Negative</th></tr>
<tr><td>0.12</td><td>1.71</td></tr>
<tr><td>2.03</td><td>0.46</td></tr>
</table>







<table>
<caption>Densities for photo 720, Azo grade 2</caption>
<tr><th>Print</th><th>Negative</th></tr>
<tr><td>0.10</td><td>1.68</td></tr>
<tr><td>1.47</td><td>0.30</td></tr>
</table>

[Chuck_1686]

Don, Have you done any step tablet tests of other papers? I was wondering how they compared to AZO.

[Mark Sampson]

Look at www.unblinkingeye.com for other peoples' Azo tests.

[Donald Miller]

Chuck, I did step tablet tests on Seagull VCFG and JandC Classic Polywarmtone (both at grade two filtration) The Seagull had an exposure scale of 1.35 and the Classic had an exposure scale of 1.15. This compared to an equivalent measurement on grade two Azo of 1.80.

For my purposes, in my system I assigned a 1.60 desired camera negative density range to the grade two Azo (subtracted .20 from the 1.80 actual exposure scale). If one were to use the same parameters for Seagull and Classic their desired camera negative density ranges would be 1.15 and .95 repectively.

Mark, I believe that if you look to Bob Herbst's work up on Azo at www.unblinkingeye.com that you will find that he used a film negative that had been exposed to a Stouffer tablet and developed and then that negative was contact printed on Azo...at least that is what the tonalities shown indicate to me. While that form of testing would be informative in some ways it would, by necessity, include the toe and shoulder characteristics of the film that he used into the test. I thought that the exposure of the Stouffer tablet directly onto Azo would be more informative of the paper characteristics since the testing that I did was to expose the paper to known and linear graduations in density.

[Jorge Gasteazoro]

While that form of testing would be informative in some ways it would, by necessity, include the toe and shoulder characteristics of the film that he used into the test. I thought that the exposure of the Stouffer tablet directly onto Azo would be more informative of the paper characteristics since the testing that I did was to expose the paper to known and linear graduations in density.



Not necessarily, information contained in the film if far greater than the paper's ability to reproduce. Even azo. The reason Herbst did a film exposed step tablet was to see how azo reacts to a pyro stain.