2016. december 28., szerda

Refreshing Collodion

The collodion mixed with halogen-salts (called: salted collodion), which is the binder material of the wet plate collodion process, start to deteriorate over time. The main reason is, that the collodion, when aged, starts to acidifying and the result is the liberation of the Iodine from its salt and then the free Iodine turn the collodion from a pale straw color to a cherry color state. The color differences would not be a big problem, but the too much free iodine (some is necessary in the collodion) makes the pictures too hard and losing its sensitivity.

My friend Attila Venczel found a paragraph of scripture about, how the old masters "corrected" this problem. The title of the book was: "Sir William de Wiveleslie Abney - Instruction in Photography".

Actually, the idea is very simple: if you have a dog that chews the rug, throw him a bone to play with.

So if you have free iodine, which chews the collodions, give it a „bone”. There are two metals considered to play the role of the „bone”: zinc and cadmium.

There are a wide variety of recipes in collodion wet process, that can help you to create a collodion solution. Each of the is the same in the way, that iodide and bromide salts (ammonium, potassium, cadmium) can be found in them. The potassium salts are soluble in water, but the cadmium salts are soluble either in water, or in alcohol. Accordingly the cadmium has been chosen because the iodine in the solution reacts with the metal cadmium and cadmium iodide is formed with this method. Since this solution is mixture of alcohol and ether, the new cadmium iodide can dissolve back to the original solution.

I chose John A. Coffer's Poe Boy collodion, as a test subject. This collodion's components are potassium bromide and potassium iodide. The biggest advantage of this collodion is its cheapness – and its major drawback is, however, that the mixture can deteriorate approx. after three months because of the reasons mentioned above.

I took to 50-50 ml from the solution, one of them was the reference, and the other is the experimental solution and I put 1gr of cadmium in solution.

After a few days it could have been seen,that the solution of cadmium started turning bright. In two weeks it has become apparent several shades lighter. After 22 days was only half as dark as the reference solution.



Then I made the first test image, and it has been  already seen on the finished picture that the "blond" collodion sensitivity is bigger, than sensitivity of the reference solution:

First test ~4 month old Poe boy - right side with cadmium

But I was waiting to see what will happen to the cadmium solution until the previous day.
I decided that I will make a final test. After 53 days, the solution got a nice straw yellow color. We should remember, that meanwhile the reference solution got older, too, it was so far nearly five months - which is well beyond the boundaries of normal usability.

Test results:

Lens: 210mm, F8
Expozition time: 40 sec.
Developing time: 15 sec.
600dpi scan



Conclusion:
The result speaks for itself, the sensitivity of the collodion improved - or stock solution  deteriorated much more. The collodion before the test began to deteriorate - although nicely executed cadmium. The collodion on the right side actually became an unspecified mixture of  potassium bromide, potassium iodide and cadmium iodide.

I think, that life of the solution could be significantly increased puttint the cadmium metal into a fresh Poe Boy mixture, preventing the destructive effects of the free iodine – and the solution could have been used much longer, than  3 months. This requires further experimentation.

I do not know, if improvement could be so spectacular under other recipe of collodion, but I think, it would make a similarly positive result.

In any case, we should not expect miracles when the collodion is already dead. It will not be like a new mix:

Lens: 210mm, F8
Exposure time on upper image: 40 sec.
Exposure time on bottom image: 20 sec.
Developing time: 15 sec.

The collodion reference picture at the bottom is about 1 month old and is made of ammonium and cadmium salts, with half of the exposure time. All conditions were the same in the case of the two photos.
In the reference image it is visible, that the rays of lights projected to the two teddybears are not completely symmetrical (little shadow on the inner half of the left side) - turn the bottles around the same light enters. The two bottle is significantly different on test image!

I think it is worth the great old masters to learn and study in their work, this is a greater treasure!



Many thanks to Venczel Attila the help so far!

Update:
My cadmium's shape is little drops. So these easy to put them in the bottle but it can be difficult to remove.


I put all of cadmium in glass test tube and heating them. The cadmium's melting point is 321°C. This is thawed quickly and I spilled it onto a glass plate. The molten metal was quickly again hard.


At the bottom of the test tube remained loss-cadmium oxide but this is not good for the conclusion of free iodine. Then I rolled up the thin stick of cadmium to snail.


It will be easy to remove any bottle!


Nincsenek megjegyzések:

Megjegyzés küldése