View Full Version : Black Dye Forming Couplers?
07-03-2012, 02:40 AM
Seen, cyan, magenta and yellow mentioned on APUG, but not black (such as for chromogenic films), anyone know what are typical black dye couplers?
Gerald C Koch
07-03-2012, 10:21 AM
AFAIK, the are no dyes that are truly black that are water soluble. There is a group of surfur based black dyes that must be created inside the fabric fibers because they are insoluble. What is perceived as black in dyed cloth is a very dark, green, blue or brown. Roughly speaking the color that a molecule absorbs is a function of its size. Unfortunately the solubility of organic molecules decreases with size. So a chemical that is truly black would be insoluble in any solvents. An example is graphite, which can be thought of as a highly condensed group of benzene rings. So what appears as a black and white chromagenic negative is actually composed of several colored dyes which when mixed approximate black.
There is an interesting experiment presented in advanced organic chemistry labs where the physical length of a long chain of alternating singe and double bonds is calculated from the absorption spectra of the compound. As the chain gets longer the color goes from red to green to violet. These compounds are of the form R-(CH2 - CH=CH)n-R', where R and R' are terminating groups and n is an integer. For a black dye n would have to be very large. Several of these compounds are used as sensitizing dyes. PE can probably discuss this aspect of these compounds further.
07-03-2012, 11:35 AM
You'd need to use a combination of Cyan, Magenta & yello9w dye couplers, their are other couplers. There was an article in a pre-WWII BJPA about the use of dye couplers for B&W use as toners and this was reprinted a few times over the years in shorter forms. I have them somewhere.
Chromogenic B&W films don't use a black, XP-2 is a brownish colour the Agfa version was even redder.