Silver nitrate contamination?

[Petzval Paul]

Hi Everyone,

I've been having a problem that's giving me trouble: my exposures are too long. At first, my wet plates were in near-geological time so, working with Denise Ross of The Light Farm, I mixed up some dry plate gelatin plates that worked great but instead of ASA ~10 I was way down maybe below ASA ~1. Then I got ahold of some B&S Old Workhorse collodion to remove a variable. I also bought some new ferrous sulfate (food grade - nice stuff! ) to rule out the developer. Still, my exposures are far longer than I would expect, although the plates are otherwise clean and fog-free. Although drowned in Georgia summer sun, my studio is full of wonderful indirect light that should be perfect for such period work, I'm over at one minute at f/4.5.

The only chemical in common between the two types of plates is the silver nitrate. I bought a pound of it two years ago from artcraft chemicals and it's been stored, as far as I can recall, in normal temperatures. Is it possible that having the dry nitrate could have been affected by fumes from another chemical??? Any ideas?

Thanks in advance for any insight that can be offered.

[Jim Noel]

I doubt seriously if it is the silver nitrate since you say the plates are clean and fog-free.

[Petzval Paul]

Well, back in '06 I had a similar problem due to some bad ether (the seller admitted selling us the 'wrong' ether and refunded our money) but, obviously, there is no ether used in making gelatin dry plates and the B&S collodion should be fine. At first I thought it might be my iodides/bromides (I've heard of these going 'bad' from other wetplaters) but the fact that I haven't had a decent exposure time in either dry or wet plate would seem to indicate that the one compound in common, silver, would be the obvious place to look. I need to get in some more silver nitrate to test, of course.

[cyrus]

There are ALL sorts of variables that can affect speed including definitely how fast you are introducing the silver nitrate into the gelatin fro dry plate, and whether it is given time to ripen enough, not to mention temp variables.

[Petzval Paul]

Yes, absolutely. I did all of that as closely as I could to the directions and even after several batches, couldn't get anywhere near the speed it was advertised as having. That's one reason why I bought some pre mixed collodion, which should be fairly consistent. Previously, I could get a negative out of an exposure of just a few seconds, now it's more like a full minute. We have lots of terrific sunlight here in Georgia, especially during the summers, so I really feel that something is fundamentally wrong.

[Gary Samson]

Have you tried shooting outside on a clear day? My exposures on a clear day on the north side of a building in shade run about 5 seconds with a f3.5 Petzval lens. I'm using the same collodion from B&S.

[Petzval Paul]

I'll give it a shot once I get a minute and check. I'll shoot an ambro to test with a f/3.6 Petzval. Good idea and thanks for the info - now I have a frame of reference for the b&s collodion!

[cyrus]

Well, other than eliminating variables one by one and that includes a new batch of silver nitrate, I can't think of other options. Considering the costs of silver, it can't be ruled out that someone along the way decided to shortchange you on the silver content. I just blew $$$ on some silver nitrate myself -- now I'm worried