Help identifying marks (wet plate collodion photography)

Hi, I work on wet plate photography and these are part of the scanned images of the plates that I recently made.
Can you identify these white and black marks (spots)?
Both of them are ambrotypes. They were not from one shoot session though.
I used a moderately new collodion and developer. My silver bath has been recently maintainanced (1 month ago).
Is it possible to have these marks (dusts?) if the plates aren't clean enough?
Thank you in advance.

D_Quinn said:

Is it possible to have these marks (dusts?) if the plates aren't clean enough?

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My experience with wet plate is that any debris or contamination will show up on the final plate or negative. In this case, it might be minor dust stuck to the plate at some stage, possibly between pouring it and developing it, contamination of the silver bath (a lot can happen to it in 1 day, let alone 1 month - also, 'maintenance' is a bit of a generic term given the many things one can do with a silver bath to recondition it) or it may be undissolved particulate matter in the developer or even fixer.

The challenge with wet plate is that the potential number of causes of defects is so huge that in a way, it's a pretty much a miracle to get a defect free plate

In your place, I'd start by reviewing the cleaning and handling procedures you use, and perhaps try a couple of glass plates (assuming these ones are black powder coated aluminum as is common for ambrotypes) to rule out any problem associated with the base material.

When I did wet plate, I also had a second silver bath standing by in case one gave me trouble. I worked on 4x5 and my silver bath was about 125ml (in a very slim tank), so I could easily afford having two baths to work with. This really helped me troubleshoot a lot of issues especially when I just started out, although I wouldn't say its strictly necessary to have two baths at all times.

Thanks for the useful comments. I’ll review all my cleaning procedures and see how it goes in my next photoshoot.

I thought the glass plates were clean enough but they actually weren’t. I always try to use calcium carbonate to clean the glass plates (yes I work on ambrotype, clear glass) but I would like to know how calcium carbonate contributes to cleaning the plates. Someone wrote in his blog says that calcium carbonate scrapes the surface of the glass and makes super fine scratches just so that collodion stays well on the glass. Would it sound true to you?
Could I use dish detergent to clean the glass?
Thanks again.

I don't believe calcium carbonate is hard enough to scratch soda-lime glass, but the scraping action of the particles will remove impurities that don't come off with detergents or scrubbing with soft materials like cotton balls.

There are optical glass cleaners that can be used (with distilled or DI water rinse) before operations like vacuum deposition coating, those would be suitable -- but they're expensive and didn't exist in the original wet plate era, so it seems likely they aren't necessary. Dish detergent (like Dawn) might work well, but I'd still apply the calcium carbonate after to ensure all traces of the detergent have been removed.

Donald Qualls said:

I don't believe calcium carbonate is hard enough to scratch soda-lime glass, but the scraping action of the particles will remove impurities that don't come off with detergents or scrubbing with soft materials like cotton balls.

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Indeed. In my experience, calcium carbonate scrubbing, a rinse and a final dust-off just before pouring the plate with a clean cloth are perfectly adequate. I've never had the need for anything more specific, although I bet there are about 100 materials and 1000 procedures that will give an equally good result

Donald and Koraks, Thank you as always for sharing your experiences and thoughts. Sounds like calcium carbonate scrubbing seems to be the best cleansing method.