Dry Plate Collodion
I do not often post on this forum because most of my experemental work these days is covered in the Silver-Gelatin Forum. I did take a workshop on Wet Pate Collodion several years ago, but did not follow through on it.
I am reading "Treatise Of Photography On Collodion" by Waldack and Neff;1856. After chapters on both Positive and Negative Wet plate Waldack adresses Dry pale Collodions. Here is where my intrest is raised. I am currently working on a panchromatic silver gelatin dry plate process. But Waldack raised my intrest when he wrote that the use of iodine salts with the bromide salts creates sensitivity to red ,yellow and amber light.
Almost all silver-gelatin emulsions contain both bromide and Iodide salts. But here the iodide increases photo-speed. It dose not yield sensitivity to green or red light. Without the adition of spectral sensitizers (specific dyes), all silver/gelatin/bromide/iodide emulsions are sensative to blue only.
My question is this. With Collodion plates,can orthochromatic or panchromatic plates be made without spectral sensitizing dyes?
My guess is "no". But I have very litlle experience with collodion, so I thought that I would ask.
Regards and thank you,
Iodide will give sensitivity in the green with dry plate emulsions. According to Mees and James (1966), silver bromide is sensitive to 490 nm and silver bromide with 3% silver iodide is sensitive to 520 nm. According to NASA http://eosweb.larc.nasa.gov/EDDOCS/W...or_Colors.html
green has a wavelength of about 510 nm.
As far as red sensitivity, I'd be interested in seeing his evidence of that. I understand that James Clerk Maxwell made the first color photo using blue, green and red filtered exposures, making reversal transparencies, and then projecting them back through the red and green filters. I can't find a reference, but I understand that he used an exceeding long exposure to make the red exposure. If you look at the graphs of spectral sensitivity of the different silver halides, I wonder if the "practical" sensitivity can be extended via filtration and long exposure...
I'm not a chemist, but the bit about red sensitivity really surprises me. I will be interested to see what Photo Engineer has to say about this.
Originally Posted by wildbillbugman
After receiving these two replies, plus one in the B&s Forun, I think that Waldack may have misinterpreded an increase in general speed of the Br emulsion with the adition of I for a broadening of the absorption spectrum. But, I would like to hear from PE on the subject.
Sticking my nose where it don't belong -I know nothing about any of this stuff- but I was actually reading some things last night in freepatents
Totally over my head
but here is a page on Silver Iodide in emulsions that I actually bookmarked -flol! Why? haha
If its of no help at all you can e-smack me.
The bright yellow silver iodide grains can selectively reduce scatter of blue light while efficiently scattering green and red light. This can have the effect of increasing the green or red speed of an emulsion while simultaneously reducing unwanted blue light exposure.
That seems related to your last post, at least.
Yes, Son of Sand,
Makes perffect sence. However, I have not yet found any "Near Panchromatic" Collodion systems that do not use both red and green sensitizing dyes. The terms "near panchromatic" or "almost panchromatic" are often used because,a collodion plate recipe was not found that ballanced the red, green and blue sensitivities to the visual spectrum. For that reason,color compensating filters were used with these systems.
Here is a question for Kirk,or anyone else who was making photographs when wet pate collodion was new.
Why so much iodide in relation to bromide? Often there is actualy more I than Br. This is never the case in silver gelatin emulsions, which contain very little I in relation to Br.
Ok, Dick Daubendiek was working on a 10 nm Bathochromic shift in absorption by Iodide using Epitaxy. The references to the work of Joe Maskasky and Gary House are just further epitaxy and uses for extended (10 nm) shifts to longer wavelengths. This gets us more green but no red sensitivity AFAIK.
However, the chart in Mees and James shows that increasing iodide leads to longer and longer sensitivity. But, in no case that I know of is there any red sensitivity. It is probably more due to "leaky" filters of the time than real sensitivity as even Maxwell's experiment was "wrong" in that his filters and dyes were not exactly what he expected.
So, as iodide goes up, longer wavelengths come into play in sensitivity, but then the emulsion becomes less developable. Epitaxy was one way to gain high speed AgCl/I emulsions with good sensitivity and still allow for fast development.
This is not to say that dry plate collodion might not be different, but the only red sensitivity that I have heard of was done with dyes and included Chlorophyll. I posted some information on that in another thread in response to Bill's prior question. That may be of some help here.
However, I have had no problem with red sensitivity using the Sands dye I described earlier, but I must add that I have been told that sensitizing dry plates is harder and different. One method makes the dry plate and then submerges it in a solution of dye. The excess is run off and the plate is re-dried. For details go to the references I posted before please.
Thank you for your great reply to my qestion.
I am not abandoning silver/gelatin emulsions. But someone at APIS sugested trying dry plate collodion.
Going through the literature from 100 or more years in the past,it is obvious that ortho and panchro plates were made by dye adition, not by an increase in iodide. That was probably a misinterpitation by Waldack.
Many of the dyes used to sensitize collodion were also used in early dry pate gelatin emulsions.
I have done only a little work with the Sands dyes because of the cost. But,if all else fails......
All of the old wet and dry plate collodion formuli have much,much more iodide salt in relation to bromide salt than any of the gelatin emulsions dicussed in the Workshop, in this forum ,or in any of the old books. I wonder what the reasoning behinde this was. Could it be that they just did not know better?