Hi everyone, I have a question which only expert emulsion makers will probably be able to answer. If there are any veteran photo chemists out there, here is my question:
I noticed that in the published versions of the "Brovira Hard" formula, a small amount of Sodium Chloride and Rhodium Chloride are added just before precipitation. I would like to know specifically what the function of the Sodium Chloride is.
It seems that the Rhodium Chloride was used to boost contrast (as many authors in the literature point out). What about the Sodium Chloride? Does it also change the contrast? Does it somehow change the colour of the final emulsion by making it warmer (i.e., by forming Silver Chloride)? Or is it there to alter the PH of the solution before precipitation and the addition of ammonia? I would really like to know.
Here are the first four steps of the "Brovira Hard" formula (as published on the FIAT/BIOS reports):
Formula for "Brovira Hard"
(1)
Gelatin (active): 500g
Water: 20 litres
(2)
Potassium Bromide: 750g
Potassium Iodide 10% solution: 100mL
(3)
Sodium Chloride 25% solution: 180mL
Rhodium Chloride 1:10000: 6.5mL
(4)
Silver Nitrate: 1kg
Water: 6 litres
Ammonia (0.910): 1 litre
[...the formula goes on...]
Please note that the 25% solution of Sodium Chloride is only used in Step 2 of the "Brovira Hard" "Brovira Normal," and "Brovira Extra Hard" formulae.
In the "Brovira Special" emulsion (a softer version), Sodium Chloride is added in Step 1 (presumably in solid form) but not in Step 2.
As for the "Brovira Soft" emulsion, there is no Sodium Chloride at all.
Thanks for any insights you might have!
I noticed that in the published versions of the "Brovira Hard" formula, a small amount of Sodium Chloride and Rhodium Chloride are added just before precipitation. I would like to know specifically what the function of the Sodium Chloride is.
It seems that the Rhodium Chloride was used to boost contrast (as many authors in the literature point out). What about the Sodium Chloride? Does it also change the contrast? Does it somehow change the colour of the final emulsion by making it warmer (i.e., by forming Silver Chloride)? Or is it there to alter the PH of the solution before precipitation and the addition of ammonia? I would really like to know.
Here are the first four steps of the "Brovira Hard" formula (as published on the FIAT/BIOS reports):
Formula for "Brovira Hard"
(1)
Gelatin (active): 500g
Water: 20 litres
(2)
Potassium Bromide: 750g
Potassium Iodide 10% solution: 100mL
(3)
Sodium Chloride 25% solution: 180mL
Rhodium Chloride 1:10000: 6.5mL
(4)
Silver Nitrate: 1kg
Water: 6 litres
Ammonia (0.910): 1 litre
[...the formula goes on...]
Please note that the 25% solution of Sodium Chloride is only used in Step 2 of the "Brovira Hard" "Brovira Normal," and "Brovira Extra Hard" formulae.
In the "Brovira Special" emulsion (a softer version), Sodium Chloride is added in Step 1 (presumably in solid form) but not in Step 2.
As for the "Brovira Soft" emulsion, there is no Sodium Chloride at all.
Thanks for any insights you might have!
