by walschuler » Thu Apr 06, 2017 12:19 pm
A progress note:
After consulting with the Olsens, who donated the plates long ago, I tried a 5 minute water pre-soak. We got images (THANK YOU R and B!), albeit not very strong ones. The OD was 1.5 and 2.0 in the trials, and the images about the same strength in them. This OD for that exposure is consistent with my memory of the last prior student experience, several years ago. We tried post-devo ferric EDTA bleach and then ascorbic acid redevelopment, standard with PFG-01 in class, and neither improved the image, in fact they weakened it. This is also consistent with memory of the performance of Ilford plates.
So several questions: Why did the water pre-soak work?
An older question: why does water presoak hypersensitize emulsions by a factor of about two? Why does TEA do that too?
Danny and Dinesh offered suggestions involving dyes and emulsion cracking which I have not yet tested, but they are on my list....
Why should Jeff's suggestions about pre-exposure dilute bleach and devo have worked and why didn't they??
I can get along empirically but really like to be able to explain my results........
An example of sorts as an illustration of explanatory satisfaction: many years ago a student came in with a sand dollar and shot a nice hologram of it, but it had a black spot on it surrounded by rings of an orderly spectrum blue-gtreen-yellow-red, totalling maybe a centimeter in diameter. Since no TEA was involved, I had some moments of what-the -heck?! Then I looked at and touched the specimen and it dawned on me that parts were still damp, and that the part closest to the emulsion was one of those, so the imbibed moisture swelled the emulsion, with the closest part depositing the highest concentration, which then decreased radially. The black area at point of near-contact was over-swollen into the UV. and thus invisible....
A progress note:
After consulting with the Olsens, who donated the plates long ago, I tried a 5 minute water pre-soak. We got images (THANK YOU R and B!), albeit not very strong ones. The OD was 1.5 and 2.0 in the trials, and the images about the same strength in them. This OD for that exposure is consistent with my memory of the last prior student experience, several years ago. We tried post-devo ferric EDTA bleach and then ascorbic acid redevelopment, standard with PFG-01 in class, and neither improved the image, in fact they weakened it. This is also consistent with memory of the performance of Ilford plates.
So several questions: Why did the water pre-soak work?
An older question: why does water presoak hypersensitize emulsions by a factor of about two? Why does TEA do that too?
Danny and Dinesh offered suggestions involving dyes and emulsion cracking which I have not yet tested, but they are on my list....
Why should Jeff's suggestions about pre-exposure dilute bleach and devo have worked and why didn't they??
I can get along empirically but really like to be able to explain my results........
An example of sorts as an illustration of explanatory satisfaction: many years ago a student came in with a sand dollar and shot a nice hologram of it, but it had a black spot on it surrounded by rings of an orderly spectrum blue-gtreen-yellow-red, totalling maybe a centimeter in diameter. Since no TEA was involved, I had some moments of what-the -heck?! Then I looked at and touched the specimen and it dawned on me that parts were still damp, and that the part closest to the emulsion was one of those, so the imbibed moisture swelled the emulsion, with the closest part depositing the highest concentration, which then decreased radially. The black area at point of near-contact was over-swollen into the UV. and thus invisible....