Herman Leonard on increase film speed with mercury

M

mkyy

Established
Local time
1:39 PM
Joined
Mar 23, 2005
Messages
117
Here is Herman Leonard's interview on NPR.

"... I use a trick that I learned from old photographic book. If you want increase the speed of your film, roll it up in a darkroom on a reel and put it in a developing tank without any developer but in the bottom of the tank, put mercury and let it stand for 24 hours and that would double or triple the sensitivity of the film ..."

Not that I am trying to do that, we got plenty of fast film available in the market. How does that work??
 
Probably not a lot of help, but from what I have read, a lot of expensive metals (don't know the proper english term, I'm sorry!) have the property of making film more sensitive. For example, I've read of film being put in a solution containing gold-salts to increase sensitivity. I'm quite sure the effect of the mercury vapours is quite similar.

You should be able to find info on sensitizing with gold if you do a google search.
 
I hope for him that his statement wasn't due to the quite considerable and permanent effects of mercury vapours on the human nervous system :)

Seriously: this is dangerous stuff. Don't try this at home.
 
If you absolutely want a speed bump, doing a peroxide vapor bath is less hazardous.
 
Mercury fuming was one of the tricks used to increase the film's speed. Ammonia vapour, sulfite, and peroxide, as Eugene said, were the others used. All in all, they fogged the film a bit. I'm not sure how slight fogging did the trick, but I'd speculate that the fog put in the extra density with an underexposed negative would need to give more printable densities.

Others like "latensification" or even a controlled pre-exposure fog gave similar effects. Then there is also post-(camera) exposure fuming which lead to the same end.

Question is, are these tricks still relevant? These speed increase methods were from a time when emulsions were different and when the fastest around was just around ISO100-200. Modern emulsions have already higher speeds to begin with. And the modern emulsion might not respond properly to the fuming or postfogging tricks.

Jay
 
Last edited:
Post-exposure fuming is basically saturating emulsion with oxygen (in case of peroxide treatment) to lower the activation threshold of exposed halides during development. Since the basic physics of BW is unchanged it should still work, although the extent will depend on developer and particular emulsion.
 
Wimpler, the vapours.

Never got to trying it myself, but it is described in e.g. Anchell's Darkroom Cookbook. If I recall correctly, you take metal(!) tank, pour in two fingers of household hydrogen peroxide, place an empty steel reel (as a spacer) and a reel with exposed film over it, then close the lid tighly. You leave it like that for a few minutes, maybe rocking the tank slightly from time to time, then transfer the film to developer. The lid should be opened carefully since vapor pressure builds up.

EDIT: OK, the vapor bath should be *after* development. An excerpt from the book can be viewed here
 
Last edited by a moderator:
I went searching for more info. I searched for sensibilisation and hypersensibilisation in my photographic encyclopedia. I found about multiple ways to increase sensitivity. Most methods can be applied both before and after exposing the film. It is recommended doing this after exposure for two reasons: 1. You can decide what EI you want to expose your film at when you are going to use it 2. These methods dramatically decrease the time you can keep film (typically 1-2 days). Also remarable is that for most methods, you can either use vapour or actually soak the film in a solution. Even just soaking film (in distilled water) is said to increase sensitivity (by increasing silver density).

The book also mentions results are not very reliable. They depend strongly on temperature and humidity.
 
Scary!

Scary!

Just to reiterate what was said above - even if you could find a source for mercury you would not want to use it. Highly toxic - especially to children. Gawd - if I tried the mercury trick at home here in the People's Republic of California they would probably arrest me.
- John
 
Mercury fuming was the key step in Daguerrotypes- the plate was 'fumed' at an angle over the warm Mercury. This is (if I'm remembering right- played with mercury a lot as a kid ya know) what made the image appear after exposure? I could look it back up if you want.
 
sepiareverb said:
...if I'm remembering right- played with mercury a lot as a kid ya know)...
Click to expand...

Yeah - me too! My dad had a pint flast in the garage he used as a weight for veneering projects. I used to pour out little blobs and play with them for hours before herding them back into the flask. Now I'm "mad as a hatter".

Times change - my kids are going to have to come up with different ways to have fun.

BTW - I thnik you are right about the daguerreotype development process - warm mercury vapors. I suppose the saying might have been "mad as a daguerreotyper" if better processes had not been invented.

- John
 
For whatever it is worth, daguerrotypists were notorious for becoming mad as hatters. And for the same reason, mercury poisoning.
This thread is interesting. I remamber reading about hypersensitizing film for astrophotography as a kid, but that is rather different. It involved 'soaking' the film in hydrogen at high temperatures. The hydrogen would replace water in the emulsion, and reduce reciprocity failure for long exposures.
 
Bryce, the astrophotography is not something different, it is the exact same thing! Also sometimes used for aerial photography, infrared photography, etc.
 
Back in the day people weren't so aware of the affects of mercury on the human body. Times were more simple, they used to let kids tour the foundry plants and let them stick their arms in the vat. Its a neat metal, and from what I hear putting your arm in the vat was a very strange sensation, like very heavy water, but it didn't get you wet or stick to your skin. To bad it can kill you/destroy your nerves, there are a lot of neat things that can be done with it. Very dangerous stuff, and the exposure is cumulative, it never really exits the system.
 
I lost a lot of Mercury balls in the cracks of the floorboards, I guess they were vaccumed up, and distributed through the air. Never had the chance to dip an arm in a vat of Mercury- wouldn't turn it down today come to think of it.

Yes those simpler times made for more simpletons, but we sure had fun.
 
Wimpler-
As I understand hypersensitization via hydrogen, it does not increase film speed. It reduces reciprocity failure, so only useful for very long exposures. So not the same as treatments that would increase effective film speeds.

Joe-
People in the 1860's were well aware that mercury could kill, though they surely didn't know as much about how or why. There is recorded information from mercury mining companies during that time- men working in the smelters were paid twice what the miners were for that reason, and still there was a shortage of employees willing to do the work.
Also, I saw a program on the television the other week on a Mayan tomb in a pyramid that had been recently discovered. The entire stone coffin was covered in cinnabar, or mercury ore, to discourage thieves.
 
Well this thread caused a GAS pain for me... I went yesterday to a used bookstore to sell off a pile of old books and found a copy of "The Darkroom Cookbook" there.
Needless to say, it came home with me.
It does say that hypersensitization with hydrogen increases film speed as well as lessening reciprocity failure... I stand corrected.
 
You must log in or register to reply here.
Back
Top Bottom