I had written earlier about the demise of Zone VI chemicals and how it has now become necessary to mix our own chemistry from raw supplies. Take a look at the previous post titled, “ROLLING YOUR OWN FIXER.” Since that post I have done quite a bit of research and testing. I am convinced that the fixer formula we chose is not exactly a direct replacement for the old reliable Zone VI product. Not that what we have been using is not a good fixer, it just is not the same. Fred always said, “Different is not the same.”
I have mixed up several concoctions, but have always come back to the Looten Acid Fixer for its simplicity and close match of pH. I kept bypassing some of the more well known formulas for some reason, possibly because everyone says they have a very unpleasant odor. I don’t believe any could be any worse than the Looten Acid Fixer we have been using. . . this stuff will take the hair out of your nose.
I want to use an acid fixer for paper, because that is what I have used for years. All I wanted to do was find a 100% replacement for the Zone VI Fixer I have used for as long as I can remember. Zone VI Fixer was stable and it had little to no odor. I have searched all over and have never found the exact published formula used by Zone VI.
I looked through all of the old Zone VI Newsletters and finally resorted to watching the Picker videos. Finally in the printing video Fred talks about his fixer being Kodak F-6. The only problem is that the Zone VI Fixer I have used for years always came in a single bag as dry chemical. If you check the formula for F-6 you will find it contains 28% Acetic Acid. I am no chemist, but as far as I know, 28% Acetic Acid only comes in liquid form. Plus, F-6 is a hardening fixer. I have no reason to believe that Zone VI is a hardening fixer, let alone all instructions for F-6 say that the hardener, Potassium Alum, must be dissolved separately and added after all other ingredients have been completely dissolved. Again, the Zone VI Fixer came in one bag containing only dry chemical. So, I really do not believe that F-6 is the correct formula for what was sold as Zone VI Fixer.
There are a lot of guesses, but I do not want a guess. I measured the pH of Zone VI Fixer to be 5.5. None of the other concoctions that I have tried matched this pH, nor did they lack a strong odor. My original choice of Looten Acid Fixer had the closest pH coming in at 5.0, but has a strong odor, where the Zone VI Fixer has little odor at all. I still found myself going in circles.
I finally got tired of having to run the vent fan on high to get away from the smell. Time to put on the apron, roll up the sleeves, and do more research. This time I decided to investigate the Kodak F-24 formula. Why I bypassed this one before is beyond me, but I did, and it was a mistake. There is an alternative mixture that is suppose to be ‘low-odor’ that substitutes Citric Acid for the Sodium Bisulfite of the original Kodak formula. This mixture still had a very strong smell. So much for the alternative, low-odor mixture!
Next, I mixed up a two liter batch of the original F-24 formula, and surprise. . . it smells just like Zone VI Fixer. Next to no odor at all. I measured the pH. . . well whaddya know. . . it was exactly 5.5, just like Zone VI. Next I needed a stability test. I put two liters of F-24 in a four liter jug and let it set for a week. No change! That does it for me. So far as I am concerned, there is no difference.
Wow! Have I solved the great mystery? Could it be that Zone VI Fixer is nothing more than Kodak F-24? I have changed our FORMULAS AREA to reflect the formula for F-24 Fixer since it is now our chosen formula for paper. Note, that the only difference in the new formula is the addition of 10 grams of Sodium Sulfite per liter to the original Looten Acid Fixer formula. Not that difficult, but it does make a difference. Even if F-24 is not the exact same formula as Zone VI, it is plenty close enough for me. I will add that Gordon Hutchings also recommends F-24 for film and paper in “The Book Of Pyro.” So, now you know what I have learned about fixer.
There is one more thing to be aware of; be very careful with the temperature of the water when mixing Sodium Thiosulfate. The most common Sodium Thiosulfate is the Pentahydrate (crystalline type) which requires 240 grams per liter. You need water at about 100-125°F, because it is extremely endothermic and will rapidly cool the water as it dissolves. This I knew from experience. What I didn’t know is that Sodium Thiosulfate Anhydrous (fine grain like table salt), which requires 152 grams per liter, should never be mixed in water above 90°F, because it will decompose and form a precipitant. Just so you know, if using Sodium Thiosulfate Pentahydrate (large crystals) use hot water. If you are using the Anhydrous (fine grain) type, mix at about 80-85°F.
CASE CLOSED. . . at least for me. I have found what I was looking for. If you were a Zone VI Fixer user and are looking for a suitable, easy replacement, this should work just fine. Now, back to making photographs. . . and. . . I can turn that vent fan down to low again!
JB
Kodak F-24
- Water (at about 125°F)…………………750.0 ml
- Sodium thiosulfate, crystalline………240.0 grams
- Sodium sulfite, desiccated……………10.0 grams
- Sodium Bisulfite………………………..25.0 grams
- Water to make……………………………1.0 liter
Note: If anhydrous thiosulfate is used, the water temperature should not be over 90°F (80-85°F) to prevent decomposition.
- Water (at about 125°F)…………………750.0 ml
- Sodium thiosulfate, crystalline………240.0 grams
- Sodium sulfite, desiccated……………10.0 grams
- Sodium Bisulfite………………………..25.0 grams
- Water to make……………………………1.0 liter
Note: If anhydrous thiosulfate is used, the water temperature should not be over 90°F (80-85°F) to prevent decomposition.