PtPd printing - trouble understanding the "restrainer"

[timgray@rogers.com]

I'm having conceptual difficulty understanding exactly what effect the "restrainer" (whether potassium chloride or sodium chloroplatinate (Na2) added to the ferric oxalate) has on the contrast of the print. Does more restrainer give the resulting positive print more contrast or less? Does it impact the entire tone curve or just the highlights or shadows? I started out with 50 50 B&S solutions 1 and 2 and changed that to 2/3 1/3 which helped with the grain, but I can't see any difference in the contrast.

Thanks for any explanation.

 

[Vaughn]

First, I like say that I try to make negatives (in-camera) that require no contrast agent. So I think that this would be your #1 goal -- to get negatives that require as little contrast agents as possible. Forget your old negatives -- make new ones just for this process. After all, you probably took the old ones with silver printing in mind, and since palladium and platinum printing is truly a different beast, you should be "seeing" differently than with other processes.

The more potassium chlorate (not chloride, btw) in the final mix, the more contrast a print will have with the same negative. This is with both platinum and/or palladium salts. The more potassium chlorate one uses (the ferric oxalate Sol #2), the grainer the print will be -- sounds like you got that scoped out okay.

If one is using just palladium salts, then NA2 will boost the contrast of a print...it will have no affect of mixes that contain platinum salts. I wasted a lot of NA2 before I found this out!

Now how they work, that is a good question...I do know, sort of, but not well enough to really tell anyone with any accuracy -- so I will let others chime in on that.

The NA2 has twice the amount of platinum ions available, or something like that...so I think it acts more like a booster than a restrainer...I think your blacks will get blacker faster, relative to the highlights, thus increasing the contrast. Potassium chlorate holds back the highlights, relative to the blacks, thus is a restrainer and increases contrast. There, I just did what I said I was not going to do -- now we wait for someone to tell me I am full of it and something else really happens !LOL!

Vaughn

 

[Kerik]

You got it half right. Potassium chlorate and Na2 are both restrainers in that the shorten the scale (ie increase contrast) by making the highlights brighter. Much less effect on the midtones and shadows. The main difference is that Na2 works MUCH better in terms of print quality, but really works best with straight palladium prints. In general, the chlorate method gives sucky results, although it works with palladium and/or platinum. As Vaughn said, it's best to get the negative right to start with. But, with pure palladium and Na2 you can pull very nice prints from negs originally inteded for silver printing.

 

[Kerik]

If you're just starting, use only palladium and add Na2 to increase contrast until you get where you want. Potassium chlorate will almost always give grainy results. Also, I recommend you use potassium oxalate as your developer rather than ammonium citrate for the most pleasing results.

 

[Paul]

If the goal is to use no contrast agents at all, is it not true that fogging will result when using only palladium and ferric oxalate Sol #1 in equal parts (i.e., omitting the Na2). Would adding a drop of 3% hydrogen peroxide fix this?

 

[Kerik]

Not necessarily if your ferric oxalate is nice and fresh. If you get fogging, a little peroxide can help.

 

[Vaughn]

Palladium-only (with no restrainer) prints can solarize. The blacks can start to lighten with excessive exposure. I have a very nice print that has deeper blacks in the image area than in the blacks in the border area (where the paper is coated beyond the edge of the negative). The base/fog and the little bit of silver in the shadow areas kept the image area blacks from solarizing while the borders began to lighten up.

If this is a problem, adding a little platinum salt prevents the solarization. The platinum in a little NA2 should do the trick, also. I normally print with a 75% Palladium/25% platinum mix. From what I understand, the added platinum will cool your print color down a little, and increase contrast a little. I have been using the 75/25% mix for so long that I have forgotten if that held true for my prints...I also changed paper and developer since I switched to the 75/25% mix, which all affects print color and contrast.

Vaughn

 

[timgray@rogers.com]

Thanks for all the input, I've been working with the ptpd mix from B&S (1/3 2/3) with the ferric oxalate 1 and 2 (1/3 2/3) for a few months, but have the Na2 kit on the way. I'll give potassium oxalate a try as a developer next time I order chemistry.