PE exposure from the base ,with yellow dye inhibiting exposure further "up" is probably why it works as a matrix film ? With more light ,proportional to the negative density,penetrating further and yeilding higher areas after hardening and clearing.
That's right Bill, the yellow dye only works for a blue-sensitive (maybe ortho too) emulsion and is specifically useful for exposing through the base and creating a "tenuous" relief. Too high a relief and you get trouble maintaining flush contact between the matrix and the receiving paper. F.E. Ives first patented this idea and used in for dichromated-gelatin (carbon) matrices. Pan-matrix film used a black dye for the same purpose.
Do these dyes have known characteristics and chemical names? What is the best reference book on sensitizing dyes? There are a lot of dyes and colorants out there being used in medical applications, and nanotech.
I'll have to get that reference. The reason I mention it is that the laser dyes and other things such as quantum dots (that work like dyes) and my own work with tuned to length centrosymmetric molecules (like carbon nanotubes in the 300-1000nm length range) would seem to offer a possible new set of useful sensitizing materials. The PV solar industry uses sensitizing dyes to move toward the red, for instance, and the dyes have to be lightfast and reasonably priced.
My own work in carbon nanotubes on SiO2 substrates supports the theory we can tune structures to various colors and enhance efficiency of PV solar using dendritic structures having electrical lengths 1/2 or 1/4 of a wavelength (not accounting for loading by adjacent structures) of the target wavelength, the idea being to make blue sensitive PV work in the red or even IR someday.
It seems similar to photographic sensitizing dyes, but with vast differences in structures. I am not the expert on this, but if you wish I can try to put you in contact with a world class expert on this subject. I would need his OK to proceed.
I'll wait until that book, which I just ordered, comes in and try to determine if there is a crossover opportunity first. It would seem to me that the PV dyes are deposited to perform the same two steps 1. wavelength-specific absorption and 2. excitonic transfer of energy to the charge receptor.
Mees and James is essential reading, and could take years, as it is so detailed. The authors lament in the introduction that they cannot discuss emulsion making - leaving that to Ron, apparently to write. Two chapters on spectral sensitizing dyes and theory. I was pleased, and astonished, that so long ago Kodak engineers knew all about what nanotechnology scientists are "discovering" today about centrosymmetric dyes and their ability to convert energy at different wavelengths. Today we have new dyes, but they work the same. This is good news and portends easier dye sensitization of our own silver halide emulsions in the future.
Today's dyes are very soluble in water and therefore are easier to handle! The ones you are reading about are from 50 years ago or so. This is (or was) so secret that we were not allowed to publish! Chemical sensitization with Sulfur and Gold was another restricted topic. I was not let on on the latest in that field until just before I retired. The emulsion scaling software was working so well that they wanted to try to build a finish scaling model based on Activation Energy in K.Cal / Mole of Silver.
Regarding what Mees says in his forward about emulsions, one reviewer of my book has stated that I have written that chapter. I want everyone to know that it is not deeply technical with lots of theory and chemistry. It is more explanatory and practical for home lab use.