Collodion Opacity and Sensitivity Inconsistency of Collodion

Hi,
I've been practicing tintype photography for about 1.5 years and have three questions. I would appreciate it if someone with extensive knowledge could answer.

When I take the plate out of the silver nitrate before shooting, the collodion sometimes appears as Silver “white” (Opaque white), while other times it is considerably weaker and thin, almost gray (on the black plate). It puzzled me, so I recently conducted tests by varying the temperatures of the chemicals, changing the room temperature, altering the method of flowing collodion, and adjusting the time between collodion and silver nitrate. However, there wasn't much change. The thickness of the collodion seems to vary.
1) What factors could influence this?

I've noticed that when the collodion is “whiter”, the image appears to look a bit brighter.
2) Does the opacity of collodion affect sensitivity?

A related question is that under nearly identical conditions (strobe light intensity, the temperature of the silver nitrate, salted collodion, and developer, the room that I am working at, and setting time for collodion before silver nitrate), I sometimes get variations of 1/3 to 3/4 stop in speed. This occurs even when shooting within an hour on the same day. I understand that wet plate photography involves various variable factors, but a difference of more than 1/2 significantly alters the impression of the image.
3)Could you please suggest any possible reasons for this exposure variation?

Note: I use 5x7 inch plates, and my collodion consists of KI and CdBr2, primarily for photographing people.

Thank you!

D_Quinn said:

The thickness of the collodion seems to vary.

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It's possible that this is indeed the reason why you see some color/darkness changes on the freshly poured plate. This could either be due to how you tilt the plate as you pour the collodion; if you keep it quite level for some time, it may settle in a thicker layer than if you tilt the plate quickly to each corner and then drain off the collodion. There may also be a difference depending on how much you pour on the plate initially, as this can influence how much time you spend distributing it across the plate.

Changes in the collodion itself might be relevant too, but if you use the same collodion mix every time, I don't expect this to be much of a factor. Maybe the temperature of the collodion and in particular the plate may matter, although I doubt it. The plate will cool off pretty quickly anyway due to the evaporation of the ether.

D_Quinn said:

2) Does the opacity of collodion affect sensitivity?

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Not as such; the collodion itself is transparent. It's the silver halide that gives it the color/tone. If you have a plate that comes out a little darker from the silver bath, this suggests that there's less silver halide on the plate. This in turn means that given the same exposure, the plate will develop less density (a weaker image) than a plate that comes out of the silver bath with more silver halide on it.

Note that the time in the silver bath, temperature of the bath, the condition of the bath (how much halides dissolved in it, its pH etc.) will all influence how fast the silver halide is formed on the plate. So it's very likely you'll see some shifts even if you think you're following the exact same procedure every time.

D_Quinn said:

3)Could you please suggest any possible reasons for this exposure variation?

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See above. It's very difficult to accurately control silver halide formation in something as crude and simple as a wet plate procedure. It's normal that there will be variations. I think to an extent it's something you'll have to learn to live with.

koraks,
thank you as always for your valuable information. It is greatly appreciated.

The two images attached were taken with the same strobe intensity and developed within a 30-minute span. There is a noticeable difference in sensitivity, about half, and I'm wondering if this is due to differences in the thickness of the collodion. I'm using the same collodion and silver nitrate for both. The hypothesis is that higher collodion density contains more silver halides, making it appear brighter while the sensitivity remains the same. Do I understand you correctly?

I have another question. I need maximum sensitivity for my portrait work, so I mix a fresh batch a few days before I shoot. I usually finish unused stock collodion(unsalted collodion I mean) within about six months, but I've noticed that aging stock collodion might affect the sensitivity of a fresh batch. Do you think storing the stock collodion in separate bottles, minimizing exposure to oxygen, would prevent oxidation of the stock collodion? I wish I could buy smaller quantities but 500ml is the only available small size here.

Do you think the aging of unused collodion has an impact on sensitivity? I read somewhere that collodion, once mixed with KI and CdBr, loses sensitivity after 1 or 2 months. So, I hadn't thought that unused collodion would affect sensitivity. In the past, to keep black and white film developing chemicals fresh, I used to elevate the liquid with glass marbles to fill the bottle, but using marbles for stock collodion seems laborious.

Any advice would be greatly appreciated.

Thank you.

D_Quinn said:

The hypothesis is that higher collodion density contains more silver halides, making it appear brighter while the sensitivity remains the same. Do I understand you correctly?

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Yes, you do. It's at least the hypothesis I based on your own suspicion that the thickness of your collodion might vary from plate to plate:

D_Quinn said:

The thickness of the collodion seems to vary.

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So that's the hint I went by. It's not the only possible hypothesis, however. As hinted at earlier, other factors also play a role in silver halide content.
And then there's also the issue of development, which can sometimes be hard to get consistent from plate to plate (although you seem like a well-trained and consistent worker to me).

D_Quinn said:

Do you think storing the stock collodion in separate bottles, minimizing exposure to oxygen, would prevent oxidation of the stock collodion?

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I really don't know. It wouldn't surprise me, but it's also possible that the collodion mixture itself ages even in absence of oxygen. In fact, I expect that in an opened bottle of collodion, there's not all that much oxygen to begin with since the ether will form a vapor blanket on top of the collodion and that should seal it off against environmental air in a static bottle pretty well to begin with. So I'm not all that optimistic that better storage is going to help much.

D_Quinn said:

I wish I could buy smaller quantities but 500ml is the only available small size here.

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I would suggest mixing your own so that you have full control over batch size. I think in your situation, it would make sense to do so. You could mix enough to last you a few weeks or so, so you're never left with very old collodion.

When I still shot wet plate, I think the longest I used my mixed collodion (variants of 'Poe Boy', usually) was for maybe a few weeks. I do recall having tried a leftover batch that had been sitting unused for 2-3 months and it was barely capable of producing an image anymore. It was essentially rendered useless and had to be discarded. Poe Boy doesn't keep very well, I understand, and other types mixed with lithium or cadmium salts may fare better. I never tried those, though. Eventuelly, they will all deteriorate.

D_Quinn said:

Do you think the aging of unused collodion has an impact on sensitivity?

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I know that old collodion tends to behave differently; it gets slow and contrasty as I recall. Adding old collodion to a fresh batch will surely affect how the entire batch will work, yes.
Note that by 'old collodion', I mean collodion that has been mixed with additional ether and bromide and iodide salts. The collodion itself, without any additional ether or salts, seems to be fairly stable, although this, too, seems to deteriorate (and potentially dangerously so!)

D_Quinn said:

using marbles for stock collodion seems laborious.

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I also think it won't help, so I wouldn't bother.

Of course, you could try and store let's say 100ml of collodion in an entirely full bottle (so use a 100ml bottle) and 100ml of collodion from the same batch in a larger bottle with air on top, and compare the performance between the two after e.g. 2 or 3 months. If there's a noticeable difference at that point, you know that the storage method does have an influence. It's an easy experiment to set up; it just takes some time.

Thank you for your advice again!

I actually make my own mix with raw chemicals (bromide + Iodide salts, ether, and alcohol). However, the minimum sale quantity of the raw Collodion here is 500ml, and if I make the entire batch into a working salted Collodion at once, the sensitivity decreases within a few months. Therefore, I usually use about 100ml of raw Collodion at a time to make a fresh batch almost every month.

I believe that ether, bromide, and iodide salts also deteriorate over time, but I suspect that the deterioration of the raw Collodion may be related to sensitivity. Collodion itself is a porous substance, and I think the formation of the image occurs when silver halide enters these pores. However, once exposed to oxygen, these fine pores may clog up, affecting the sensitivity. I'm not sure.

Your experimental idea is definitely worth trying. The next time I purchase raw Collodion, I plan to save the leftover amount from the first batch in a 100ml bottle and investigate how it affects sensitivity.