What is the point of collodion?

[Photo Engineer]

Think ETHER!

I've kept in touch with the thread John, but it is never wrong to remind people that they have a hazard around. And then again, nitrocellulose is quite flammable and can be explosive. It burns underwater.

PE

 

[removed account4]

Think ETHER!

I've kept in touch with the thread John, but it is never wrong to remind people that they have a hazard around. And then again, nitrocellulose is quite flammable and can be explosive. It burns underwater.

PE

couldn't agree with you more !

sure does ! ( burn underwater )
its used as propellent charge and explosive charge in the munitions industry !

 

[falotico]

Nitrocellulose or collodion was used to produce most of the photographs we have from the Civil War. Unfortunately it doesn't mix with water. In order to bath it in the aqueous solutions needed to sensitize the plate and develop the image, the exposure and the development were made while the nitrocellulose was still fluid. While the nitrocellulose was still "wet" it would permit water-containing solutions to flow between the nitrocellulose molecules and react with the silver iodide crystals. The glass plate was coated, dipped in silver salts to sensitize it, exposed in the camera, developed and fixed while the nitrocellulose was still tacky or "wet". The procedure was called the "wet plate process". It required development within minutes after exposure.

Nitrocellulose was used because it did not react with iodine. Early photography used iodine as the halide to form silver salts which were light sensitive. But if you mix silver iodide with gelatin the crystals are not light sensitive--they cannot be developed. The iodide attaches to the positive gelatin and prevents the reduction of the Ag+; sometimes this is called a "hydrosol". That is why gelatin emulsions almost always use bromine, not iodine. But bromine did not become commercially available until about 1860.

 

[Peter Rockstroh01]

Do contemporary Nitro lacquer formulas work ? They should have better optical and mechanical properties than the formulas I've read about ?

 

[Photo Engineer]

Gelatin does not react with Iodide. Iodide is used in most all film emulsions and pure Iodide emulsions in gelatin exist and can be developed. I have seen it done.

Peter, you might want to see some of the formulas published by Mark Osterman of George Eastman House, now the Eastman Museum (renamed last month by a new director).

PE

 

[falotico]

My thanks to PE for his response to my post on silver iodide (AgI) emulsions. There are only a handful of people on the planet who can equal his experience and knowledge in silver halide photography and I stand second to none in my respect for his opinions.

I had gotten my understanding of AgI hydrosols from Dr. J.S. Friedman's "History of Color Photography"; in particular Chapter 21, DYE TONING. In my edition the chapter starts on p. 327 and the discussion of AgI hydrosols begins on p. 340 with the text on Brewster mordants. Silver grains can be oxidized by KI solutions and made into colloids--hydrosols--of AgI which will mordant the positively charged bodies of basic dyes. Since gelatin is also positively charged, I naturally assumed that there is an interaction between the AgI hydrosol and the gelatin. However, upon closer reading I can find no mention of interaction between gelatin and AgI hydrosols in Friedman or in other sources. But please note that collodion is negatively charged and thus would have no interaction with the also negatively charged AgI hydrosols.

Friedman does mention on p.341 that the gelatin does become softened by strong solutions of KI. Brewster in his patent on the AgI mordant, US Patent 2320028, mentions that gelatin will dissolve in strong solutions of KI. Wet plate photography often used acid developers. The low pH and the release of iodide anions might have softened the early AgI gelatin emulsions causing loss of image or otherwise making them difficult to develop. Collodion is a stronger material and can withstand the acid developers and not produce excessive softening from any strong I- solutions produced. I have no published source indicating whether gelatin AgI emulsions are susceptible to the formation of AgI hydrosols, but I wouldn't be surprised if this does happen.

 

[Roger Cole]

"toxic, flammable and fugitive" - in the back of my head I knew there was some hitch. Thanks for your answers.

Great name for a rock band, "Toxic, Flammable, and Fugitive!" - now featuring guest artist, the Oxford Comma!

 

[fdonadio]

Great name for a rock band, "Toxic, Flammable, and Fugitive!"

I could be the drummer...