Type of print?greenspun.com : LUSENET : Large format photography : One Thread
Can someone define for me a Silver Chloride Contact Print? I understand the Gelatin Silver and Chlorobromide print designations, but I saw references to this type of print in B/W magazine and cannot figure out what it means. Thanks, Bob
-- Bob moulton (email@example.com), April 26, 2002
Printed on Azo.
-- wb (firstname.lastname@example.org), April 26, 2002.
A silver chloride print is not necessarily an Azo print. I know Michael and Paula like to refer to their Azo work as silver chloride; I guess it adds to some degree of mystery. Anyway, there are several classical paper types that can defined as silver chloride: salted paper, albumen and POP. The idea is that the paper is coated with some sort of salt, usually ammonium or sodium chloride, and is then sensitized with silver nitrate. In order to make the paper light- sensitive, an excess of silver ions must exist, but in essence the paper, when light sensitive, ends up coated with silver chloride and sodium nitrate.
While we're on the subject, I'd like someone to explain to me how a silver chloride paper (read AZO) may not a printing-out paper. All the above referenced papers are printing-out papers. That's the way silver chloride works when there is an excess of silver ions. Is AZO different because there is NO EXCESS of silver? Or is there some other compound at work here (like silver chlorobromide)?
-- Chad Jarvis (email@example.com), April 27, 2002.
My understanding is that POP (salted prints, Centennial etc) and DOP (Azo) silver chloride papers are mainly different in the way the image is formed. POP relies on light alone (and huge amounts of it). DOP depends upon a developer to locate latent image specks and develop those to a stronger image. In practical terms, this means DOP can have much higher speeds than POP processes.
The excess silver nitrate is POP is required to increase sensitivity and to produce a "strong" image (without the excess silver nitrate, images are grey and quite weak). The leading hypothesis is that light energy dissociates each unit of silver chloride and the chlorine that is liberated simply unites with the silver nitrate present to form new silver chloride. Light breaks down this newly formed silver chloride, and the cycle begins again, to be repeated over and over. When excess silver nitrate is available, more image silver will be formed and a greater maximum density attained. DOP papers (Azo is supposed to be a chloride paper, not chlorobromide) do not need this excess nitrate since they rely upon chemical development to strengthen the image.
I'm sure you've seen this link - it discusses lots of interesting qualities about the prinintg out processes, including discussions of how the colloidal nature in POP produce such distinctive colors.
-- N Dhananjay (dhananjay-nayakankuppam@Uiowa.edu), April 27, 2002.
Azo is a silver chloride paper, NOT chlorobromide. N. Dhananjay explained it better than I could have.
-- Michael A. Smith (firstname.lastname@example.org), April 27, 2002.
Which part of the phrase "silver chloride contact print" don't you understand, the "silver chloride" part or the "contact print" part? If it's the silver chloride part, as others have explained, that's a reference to the type of paper on which the photograph is printed. If it's the contact print part, the term "contact print" refers to a print made by placing the negative in direct contact with the paper and exposing the paper, so that the resulting print is the same size as the negative, as opposed to placing the negative in an enlarger and making the print by projecting an enlarged image of the negative through a lens and onto the paper so that the print is larger than the negative (if I'm talking down to you here, my apologies).
-- Brian Ellis (email@example.com), April 28, 2002.