Question Regarding Spot Issues: Possible Causes and Solutions, Pinholes, Comets, or Dust?

[D_Quinn]

Hello.
I have a question about a spot-related issue. Please click the below links to see the images.

①Ambrotype with the spot issue
https://photos.app.goo.gl/w9rCQV5TNwcQBoi88

②Tintype
https://photos.app.goo.gl/qjUSxEjGSBPyVoeJ7

I took the ambrotype first and then, 30 minutes later, I took the tintype (using the same collodion and silver nitrate). While there are many spots on the ambrotype (spots appear white viewed as positive image and black viewed as a negative image), there are no spots on the tintype.

Could this be due to pinholes or comets? As far as I understand, pinholes should appear as black spots in positive images. Also, the silver nitrate solution has undergone relatively recent heavy maintenance. The salted collodion is only two weeks old.

If it's not pinholes, my guess is dusts on the glass plate or collodion although I cleaned a lot. Does any one can think of other possible causes from the experience?

Any insights or advice would be greatly appreciated.

 

[koraks]

The spots are high density, so they're not pinholes. They're tiny concentrations of metallic silver on your final plate. They're not really comets, either, because those tend to have distinct trails. Comets tend to originate from particulate matter in the silver bath that deposits onto the plate as it's sensitizing and the stuff will consequently run down along the plate surface while the plate sits in the bath. Alternatively, they can be particulate matter deposited on the plate prior to development and the comet trails emerge as the developer is poured on top of the plate.

Although your plate defect doesn't look like comes due to the lack of a trail, the origins may still be the same. However, since they seem to be static (no trails), I lean towards either some form of dust left on the plate before the collodion is poured on, or a contamination in the collodion itself. The latter seems less likely because your tintype is clean while your glass plate isn't, pointing in the direction of your glass preparation.

Some questions:
1: Are your tintypes always clear of this defect? And does the defect always/often occur on your glass plates? I.e. is there a clear relationship between the plate type and this defect?
2: How do you prepare your glass prior to pouring on the collodion?

Nice photos btw. Your exposure is spot on!

 

[D_Quinn]

Thanks, koraks, as always for the clear explanation.
To answer your questions,

• Yes, this particular defect never occurs with tintypes. It always happens with glass plates.
• I always clean the glass plates and apply the albumen solution along the edges a day before the photo shoot. Then, I store these plates under a food umbrella. Before pouring the collodion for each shot, I take a plate out from the food umbrella and blow off any dust from the glass. However, I often become so focused that I forget to check.

Perhaps I should consider wiping off the glass and applying the albumen solution immediately before each shot.

Could you give me your thoughts on this, please?

Thank you

 

[koraks]

Thanks for the additional explanation. It does leave me wondering about your cleaning procedure. For instance, I used to prepare my glass as follows:
* Cut to size, and bevel the edges slightly to prevent cuts
* Wash with soap
* Buff plate with a paste made of calcium carbonate and water
* Rinse plate, thoroughly removing any traces of calcium carbonate
* Dry plate with a clean towel; set to allow traces of moisture to evaporate
* Blow off dust
* Pour collodion etc.
When batch-cleaning plates, I would store them with sheets of paper in between the plates in a box so they couldn't collect dust.
I noticed that any traces of calcium carbonate on the plate would result in density defects in the image; due to somewhat rough edges to my home-cut plates, I had to be very careful rinsing the calcium carbonate off of the plate edges or I would get 'oysters'.

I think leaving the plates out (even if covered by something) brings the risk of stuff landing on the glass surface. Even minute particulate contamination may result in density defects, especially if they happen to somehow promote activation of silver halide. I'd be tempted to try and shoot a few plates that you clean and then use immediately, without having them sit around. You may have to forego the albumen step for these tests. Btw, I never found the albumen coating along the edges to be necessary with properly cleaned plates, but I do recognize the challenge of frilling along the edges especially on plates that are not thoroughly degreased.

 

[D_Quinn]

Thanks for the additional explanation. It does leave me wondering about your cleaning procedure. For instance, I used to prepare my glass as follows:
* Cut to size, and bevel the edges slightly to prevent cuts
* Wash with soap
* Buff plate with a paste made of calcium carbonate and water
* Rinse plate, thoroughly removing any traces of calcium carbonate
* Dry plate with a clean towel; set to allow traces of moisture to evaporate
* Blow off dust
* Pour collodion etc.
When batch-cleaning plates, I would store them with sheets of paper in between the plates in a box so they couldn't collect dust.
I noticed that any traces of calcium carbonate on the plate would result in density defects in the image; due to somewhat rough edges to my home-cut plates, I had to be very careful rinsing the calcium carbonate off of the plate edges or I would get 'oysters'.

I think leaving the plates out (even if covered by something) brings the risk of stuff landing on the glass surface. Even minute particulate contamination may result in density defects, especially if they happen to somehow promote activation of silver halide. I'd be tempted to try and shoot a few plates that you clean and then use immediately, without having them sit around. You may have to forego the albumen step for these tests. Btw, I never found the albumen coating along the edges to be necessary with properly cleaned plates, but I do recognize the challenge of frilling along the edges especially on plates that are not thoroughly degreased.

Thank you for the detailed explanation. As you say, dust is the most likely cause I tend to forget to take a closer look at the surface of the glass plate before pouring collodion, especially when I have my sitter waiting for the shoot. It's a good idea to conduct some tests for cleaning the plates just before pouring the collodion.