sanking
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After the recent thread on the amount of UV blocking density needed to produce paper white with pure palladium (no restrainer) I decided to test this again in my own working space.
For the test I mixed fresh 25% potassium oxalate developer and fresh solutions of 5% citric acid clearing baths. The palladum chloride was mixed some time ago according to the formula in Dick Arentz' book. As recommended by Michael Mutmansky I used an aged ferric oxalate solution. It was actually mixed last November or December from some B&S ferric oxalate that Clay sent me. It was kept in solution at room temperature for a few weeks, but frozen in late December and just thawed out yesterday.
Humidity of the workroom was 50%, with another 15% added for total of 65%. I single coated a sheet of COT 320, with no oxalic acid bath, with a solution of 1:1 PC + FO, using 2ml per sheet of 8X10.
Examination of the step wedge print, was was made withi a 31-step Stouffer transmission wedge, was 200 units with my UL-28 plateburner.
Examination of the print, when dry, shows that when there was paper white of log 0.06 at Steps #30 and #31, there was visual Dmax of log 1.45 at Step 5, for a total range of 26 steps, or log 2.6. I went a step further and determined that when there was paper white at Steps #30 and #31, as measured by reflection densitometer, the absolute density increased from 1.45 at Step 5 to log 1.47 at Step 31. I also measured with a transmission densitometer and determined pretty much the same thing -- i.e. when paper white was at Steps #30 and #31 maximum density was at Step 5, at log 1.70, even though absolute maximum density did increase to log 1.73 at Step 1.
In an absolute sense the density needed in my tests to give paper white is log 3.0, but in a practical sense the range needed was log 2.6.
BTW, my procedure is to begin the exposure at exactly 15 minutes from the end of coating. Drying is accelerated by the use of a small fan aimed at the coated paper, at a distance of about 6 feet. Waiting longer will result in a loss of Dmax. Exposing at 10 minutes from the end of coating will increase Dmax, but at risk of paper not being completely dry. These comments apply only to my conditions, at temperature of 72F and RH of 50%.
Sandy King
For the test I mixed fresh 25% potassium oxalate developer and fresh solutions of 5% citric acid clearing baths. The palladum chloride was mixed some time ago according to the formula in Dick Arentz' book. As recommended by Michael Mutmansky I used an aged ferric oxalate solution. It was actually mixed last November or December from some B&S ferric oxalate that Clay sent me. It was kept in solution at room temperature for a few weeks, but frozen in late December and just thawed out yesterday.
Humidity of the workroom was 50%, with another 15% added for total of 65%. I single coated a sheet of COT 320, with no oxalic acid bath, with a solution of 1:1 PC + FO, using 2ml per sheet of 8X10.
Examination of the step wedge print, was was made withi a 31-step Stouffer transmission wedge, was 200 units with my UL-28 plateburner.
Examination of the print, when dry, shows that when there was paper white of log 0.06 at Steps #30 and #31, there was visual Dmax of log 1.45 at Step 5, for a total range of 26 steps, or log 2.6. I went a step further and determined that when there was paper white at Steps #30 and #31, as measured by reflection densitometer, the absolute density increased from 1.45 at Step 5 to log 1.47 at Step 31. I also measured with a transmission densitometer and determined pretty much the same thing -- i.e. when paper white was at Steps #30 and #31 maximum density was at Step 5, at log 1.70, even though absolute maximum density did increase to log 1.73 at Step 1.
In an absolute sense the density needed in my tests to give paper white is log 3.0, but in a practical sense the range needed was log 2.6.
BTW, my procedure is to begin the exposure at exactly 15 minutes from the end of coating. Drying is accelerated by the use of a small fan aimed at the coated paper, at a distance of about 6 feet. Waiting longer will result in a loss of Dmax. Exposing at 10 minutes from the end of coating will increase Dmax, but at risk of paper not being completely dry. These comments apply only to my conditions, at temperature of 72F and RH of 50%.
Sandy King
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