What actually happens in a Lumen print - photochemically ?
I've made lumen prints on and off for a bit now, and researched the best ways of fixing, toning and whatevering them, but the one thing I've never understood is the actual chemical changes that are taking place in the emulsion layer(s) of the paper that produce the effects we see.
Rather obviously, we know that silver halide emulsions, upon exposure to light, form development centres to create a latent image which can then be developed.
So is it that the gross overexposure that a lumen print receives forms an enormous amount of development centres, so much so that the image moves from latent to visible without development?
Or is there some other mechanism involved?
What about the colours? I'm guessing that this is less to do with the silver than the other "stuff" that makes up a paper emulsion ... or is my guess wildly off-kilter?
Obviously there are a lot of variables involved - often lumen prints are made with fresh plant material and there is therefore (?) in those cases some interaction between paper and sample triggered by moisture and/or the plant's own chemical compounds.
I'm setting aside from my questions those papers with incorporated developer, by the way, because that brings in a little heap of mechanisms all of it's own.
So, it would be nice to hear from those in the know about paper emulsions ...
I have no idea about emulsions and such things, but I would love to see your results. I am starting out myself with lumen now.
I am just about to see the result of an ivy that has spent a couple of hours on a Agfa paper in the autumn sun.