This is a representative print of the best of the latest work I've been doing. More widely, I have been using different combinations of palladium chloride and silver nitrate with a variety of reducing agents (borohydride, dithionite, UV radiation, ascorbic acid) and matrix materials (silica, gelatin, chitosan). I would say in summary it's very easy to produce dense images with a strong brown sepia tone, with yellow and sometimes red highlights. It has proven very difficult to find a formulation that gives a dense, neutral tone print. According to the literature, it's all about the size and distribution of the nanoparticles. I have again added poly(vinylpyrrolidone) as it is know as a nanoparticle stabilizer.
If anyone is following along, the developer is recipe 143 (detailed previously) and the paper is a new recipe (reference 212) which is prepared as follows:
10g silica solution
under continuous stirring:
add 1 drop 10% PVP
trace of sodium borohydride (I'll have to determine the exact quantity later and report, but it's too small to measure directly with my regular scale)
Stir well
add five drops of 0.1% PdCl2/HCl solution (again while stirring)
Coat onto 8x11.5 waterproof paper with a 4 micron coating bar, using about 0.5ml - 1ml per sheet. Allow to dry flat then cut into 4.
I realize that "five drops" is an inadquate specification for others to reproduce exactly, so at some point I will try to measure the equivalent mass.
I have been using this with Fuji x-ray film type HR-U. This film gives results 5-7 stops faster than the Ilford multigrade paper. The print below was at f/4.7, nominal shutter speed set between 1/50 and 1/100 seconds. This compares with manual timing of 4 seconds for the Ilford paper. I repeat that the shutter is old and may run slow - I have not measured its actual exposure time.
Procedure
When ready to print a (5x4) negative, the paper has a narrow bead of developer applied at one edge, and the film is superimposed exposed-side-down over it. Then they are fed together through an office laminator (on the 'cold' setting) inside an improvised developing pouch (two sheets of the same waterproof paper will do, taped together at the short edge). A short strip of Kleenex placed in trail to the positive/negative sandwich will absorb excess developer and help to stop it leaking out all over the rollers. The machine takes about 60 seconds to roll through the complete 8.5x11 assembly; the negative and positive are separated a further 60 seconds after the pouch clears the machine.
Comments
When coating the paper, a 4 micron coating bar gives a good glossy finish. A 1 micron coating bar works too, and dries faster, but is not as dense, and the finish is more matte.
No rails are used to spread the developer; the considerable pressure from the laminator machine spreads the developer very evenly, and the thickness of the emulsion and coatings on the paper and film seem to absorb a quantity of developer and solvent sufficient to complete the relevant reactions while they are in contact. When the negative and positive are separated, the positive comes away touch-dry instantly. The prints are robust and rub-resistant.
The quantity of developer needed for a 5x4 sheet is less than 250mg. A 25g batch of developer is good for about 100 prints, therefore. This process is very economical with the materials.
Aside from an instant print, this process produces an instant negative too - it is well developed and looks like it will print nicely. The negative needs a fixer bath, not least to remove the undeveloped silver halide from the reverse, since x-ray film is emulsion coated both sides. Then wash it in water, as you would expect. The emulsion is very fragile while wet and scratches easily, but only the one side with the image needs to be protected.
The print and negative are very grainy. I don't yet know if this is a feature of the film, or the developer. Probably both.
There is a yellow (and sometimes purple/pink) cast to the highlights, which appears after the print fully dries. The silica appears to be stained to a creamy yellow colour by the high level of hydroxide in the developer, leading to the yellow cast, and I think the pink is the trace of metol oxidizing. You can see a pink band on this print - and the fact that it is a band suggests it can be got rid of.
Some other silica-based formulations I have been using show a tendency to lose efficacy some number of hours or days after the paper is prepared. That is - paper a few days old gives a much weaker image. I will be checking over the next few days if that's the case here.
I will now work on some different developers and see if a less grainy print can be achieved, with a more neutral tone. Good luck to anyone who tries this.