One goal I have for this summer is to make a controlled precipitation using vAg measurement and peristaltic pumps controlled by an Arduino. It's rather difficult to find KNO3 for a salt bridge that isn't contaminated with chloride (one source I found was quoted at 300 ppm Cl-. By a quick back of the envelope calculation, I guess that would amount to 0.17 mg of NaCl equivalent if you needed 100 mL of 0.1 M KNO3 -- so I guess this would be negligible).
But before I get to this, I have a few more elementary problems to overcome!
I've been having some difficulty with my emulsions when processing. I'm using gelatin from Photographer's Formulary and I'm making the grade 2 azo-type emulsion from PE's book. Instead of using the 5.0 mL of 4% glyoxal as PE suggests in the book, I used 0.5 mL of 40% glyoxal, delivered with an air-displacement micropipette. I've calibrated the pipette and verified that it can consistently deliver 0.5 mL to within 5%. I've controlled the temperature of the processing solutions reasonably carefully to 20 deg. C. The paper is Strathmore Smooth.
I develop in home-mixed Kodak D-72 (Dektol), so it contains a good deal of carbonate, which I've heard may cause problems due to the evolution of CO2 in the presence of acid.
At first I tried using a weak stop bath (1% acetic acid) and fixing in Photographer's Formulary TF-4. I didn't notice any problems until the print went into the fixer. Small "blisters" of what appears to be granules of undissolved gelatin appeared. I performed the check described by PE in his DVD set to ensure that all of the gelatin was completely dissolved/melted (no gel slugs), so I can rule out that possibility. This is what the emulsion looked like after coming out of the fixer:
After washing and drying, the print looked mostly ok, albeit with some additional texture.
I then decided that perhaps I shouldn't use an alkaline rapid fixer, so I mixed up a package of Kodak fixer (powder) which has a hardener mixed in. This time, I got large bubbles inflating. Sometimes this occurred when the print went into the stop bath (again, 1% acetic acid). Sometimes the bubble(s) did not appear until the print went into the fixer. Both these solutions are acidic, so I perhaps these are bubbles of carbonate. I could hear the gelatin "squealing" as gas was released from the emulsion. There were only a small number of these large bubbles: either 1, 2 or none. The paper was the same as the above paper, but it had aged by approximately 1 month. Here's what the large bubbles look like:
Both photos are 4x5 prints. The bubbles in the second photo are about the size of a dime.
Should I give up on Dektol? Or is it a problem with my hardener? Any advice is much appreciated.
But before I get to this, I have a few more elementary problems to overcome!
I've been having some difficulty with my emulsions when processing. I'm using gelatin from Photographer's Formulary and I'm making the grade 2 azo-type emulsion from PE's book. Instead of using the 5.0 mL of 4% glyoxal as PE suggests in the book, I used 0.5 mL of 40% glyoxal, delivered with an air-displacement micropipette. I've calibrated the pipette and verified that it can consistently deliver 0.5 mL to within 5%. I've controlled the temperature of the processing solutions reasonably carefully to 20 deg. C. The paper is Strathmore Smooth.
I develop in home-mixed Kodak D-72 (Dektol), so it contains a good deal of carbonate, which I've heard may cause problems due to the evolution of CO2 in the presence of acid.
At first I tried using a weak stop bath (1% acetic acid) and fixing in Photographer's Formulary TF-4. I didn't notice any problems until the print went into the fixer. Small "blisters" of what appears to be granules of undissolved gelatin appeared. I performed the check described by PE in his DVD set to ensure that all of the gelatin was completely dissolved/melted (no gel slugs), so I can rule out that possibility. This is what the emulsion looked like after coming out of the fixer:
After washing and drying, the print looked mostly ok, albeit with some additional texture.
I then decided that perhaps I shouldn't use an alkaline rapid fixer, so I mixed up a package of Kodak fixer (powder) which has a hardener mixed in. This time, I got large bubbles inflating. Sometimes this occurred when the print went into the stop bath (again, 1% acetic acid). Sometimes the bubble(s) did not appear until the print went into the fixer. Both these solutions are acidic, so I perhaps these are bubbles of carbonate. I could hear the gelatin "squealing" as gas was released from the emulsion. There were only a small number of these large bubbles: either 1, 2 or none. The paper was the same as the above paper, but it had aged by approximately 1 month. Here's what the large bubbles look like:
Both photos are 4x5 prints. The bubbles in the second photo are about the size of a dime.
Should I give up on Dektol? Or is it a problem with my hardener? Any advice is much appreciated.
