Regarding black spots/ collodion flaking?

D_Quinn

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This is an ambrotype (5x7 inches) I shot today. It looks like the collodion has flaked away in small spots here and there, especially around the edges of the plate. What do you think could be the cause?

The room temperature was quite high at 28°C, which resulted in a lot of fogging, and when I wiped the plate during the water rinse with cotton, it might have caused some of the flaking, but I only noticed it after everything had dried. It happened before but I couldn't find the cause when that happened.

Anyways it’s possible that I waited too much time after applying the collodion and submerging the plate in the silver bath (about 50 seconds), causing the collodion to dry from the edges, but I’m still not sure of the exact cause.

If you have any suggestions or hints that might help solve this, I would appreciate it!!

Many thanks!
 

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retina_restoration

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My guess is that you've abraded the collodion with the cotton ball. You have to apply VERY little pressure to perform this task. Basically, you dangle the wet cotton over the plate and allow only gravity to apply pressure to the surface. Do not press!
 
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D_Quinn

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Thank you for the advice! This has happened several times with ambrotypes, but I don't think it has occurred with tintypes. Do you think collodion is more likely to peel off with ambrotypes?
 

koraks

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retina_restoration said:
So, I should ask: how are you prepping glass for pouring the collodion? That step is extremely important for getting collodion to adhere properly.
Click to expand...

I agree; this is likely the key issue in this flaking problem.
I've found that collodion adhesion to glass is fairly good and will withstand careful wiping with e.g. a cotton ball, provided that the glass is very thoroughly cleaned/degreased beforehand.
 

retina_restoration

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And preferably treated with a 1/8" band of dilute albumen on the edges.
 
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D_Quinn

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Thanks for your comments!

I am relatively careful when preparing the glass plates. First, I scrub both sides with a solution of calcium carbonate and alcohol dissolved in water, then rinse it off with tap water, and do a final rinse with distilled water. Once dry, I blow on the plate and wipe it with a cotton cloth just enough to avoid leaving streaks. After that, I apply albumen about 1/2 inch (6mm) wide along each edge. I make the albumen all at once and freeze it for later use (since it molds in the fridge after about three months). Japan is so humid!
If there is anything concerning about this procedure, please let me know.
 

retina_restoration

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Your process sounds good, but there's no need to make a full half inch band of albumen around the edges - 1/8" is plenty. Even 1/16th inch works fine as well. Making a really wide band of albumen can create problems sometimes; it can interact with the collodion to create unwanted artifacts. It's best to make the width of your band of albumen as narrow as you can.
 

koraks

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D_Quinn said:
If there is anything concerning about this procedure, please let me know.
Click to expand...

Sounds good and actually more thorough than I used to do it.
I notice that the defect you posted seems to run right along the line where your albumen edge gives way to pure glass. Have you tried omitting the albumen edges? I never did that, and it worked OK without. I'd suggest only introducing the albumen edges if you have problems with collodion peeling away from the edges.
 
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D_Quinn

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Thank you for the comment! Next, I’ll try narrowing the albumen application width just a little and also try not applying albumen at all to see if the issue occurs. It does seem like the defect is happening along the width where I applied the albumen.
 
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