Palladium Chloride Mixing

[Michael Mutmansky]

Think of it this way... When you mix equal parts of the traditional PD solution and the traditional FO mix for PD, you are essentially matching up the proper amounts of the various chemicals in solution that then dries on the paper. The concentration of that combined solution is fixed based on the amount of the chemicals in the two component solutions, and the presumption that you mix them 1:1. I've done the tests, you do want to mix them 1:1 when using the standard solutions.

If you increase the concentration of the PD from 10% to 20%, you will effectively have twice as much PD in the solution, so you only need 1/2 as much solution to achieve the proper amount of PD chemicals in the combined FO-PD mix. That means that you can make the same effective solution using 1:.5 mixes, instead of 1:1.

Now, consider that the paper can only handle so much solution per square inch (square foot, whatever). Lets say that you are limited to 2ml of solution per square foot. Normally, that would mean that you would do 1ml of FO, and 1ml of PD (10%) to get the proper 2ml total to cover.

However, if you use 20% PD, you only need .5ml to make the proper balanced FO-PD solution, so you end up with only 1.5ml of total solution. That may not be enough to cover properly, so you could add .5ml of H2O to bring it up to 2ml total, or you could add more FO and PD solutions to create a combined mix that added up to 2ml total. If you add more PD and FO, you ultimately get a condition where the two end up have a higher concentration PER SQUARE INCH on the paper, and it doesn't overload the paper with too much liquid.

You would have to use a 2:1 ratio of FO:PD to keep everything proper (because the PD is 2x as concentrated as the FO compared to the traditional formulas), so to get a full 2ml of mixed solution, you would want 1-1/3 FO and 2/3 PD to keep it balanced and at the proper total amount.

This ultimately results in a solution that is 1.3X more concentrated, so there is 1.3x as much useful chemical PER SQUARE INCH when the solution is dried into the paper.

If you can do a PD solution at 30% (which you should be able to, if I remember correctly) you would need 1/3 as much PD as FO. That works nicely, as the two combined equals 4 parts (3 parts FO and 1 part PD), which is normally easily calculated and measured if you are using pipettes, and even if you are using droppers. That would result in a solution that is 1.5x more concentrated on the paper. You would do 1.5ml of FO and .5ml of PD to achieve the proper amounts (achieving a 3:1 ratio, 2ml of total solution, and 1.5x the 'traditional' amount of PD in the mix)

And it can be done in one coating, rather than two coatings. The benefit is that it can be done in one coating in my mind. In my experience, single coating is much more consistently 'perfect' than double coating, so if you are looking to get a DMAX boost but wish to avoid coating flaws that sometimes come up because of double coating, this is a good way to do it.

Or, you could be really indulgent and double coat with the higher concentration solutions, but I doubt the payback in improved DMAX is worth the cost. You'd probably have a lot of wash-off.

Don't try to increase the FO percentage; it's near saturation, and it just won't be possible to get any more into solution properly.

---Michael

[Kerik Kouklis]

I see that B&S offers a "Palladium Chloride No.3 Standard" mix that is a 15% solution.

You might want to check with them on this. They describe it as Sodium Chloropalladite 15% solution (aka sodium palladium chloride). That does not mean it contains 15% palladium.

The formla I gave is ~15%

5 gm Pd + 3.5 gm NaCl = 8.5 gm in 55 ml of solution.

8.5/55 = 15.4%

[Harald Leban]

Craig,
it´s a fact that one cannot compare percentual concentrations so straight - chemistry uses a different system - the molarity . A 15% Palladate solution is around 0,5mol/l and a 30-35% FEO is around 1,5mol/l, so when using equal quantities for coating and knowing that you need 2mol of Fe(III) to reduce 1mol of Pd(II) you still have 50% FEO over.
If you like to use higher Palladate concentrations you should make the Ammonia salt instead of the Sodium compound (change the Sodiumchlorid against Ammoniumchloride) it will reach solutions up to 20% and higher without precipitation.
There could be troubles in increasing the FEO concentration because of lack of solubility.

I found a slightly different compound "Ferricoxacitrat" as a better choice for working with higher concentrations and deeper d-max......

allthebest

Harald

[Michael Mutmansky]

Harald,

That may be true, I'm not a chemist. However, I have done the tests to know that the FO to PD proportions are essentially optimized when the 'traditional' formulas are used without alteration.

Essentially, DMAX decreases if you deviate in either direction substantially.

[Harald Leban]

Michael,
the reason why it works with the traditional formula is because it´s well balanced in concentration. But double % concentration means also double molarity (if we put the increase of liquid density by side) - so your calculation is right when you decrease the quantity of Palladate in the same ratio you increase the concentration of it.

What I tried to explain is that some must use a higher Fe concentration to work with a more concentrated Palladate to reach a higher sensitizer concentration on the paper and finally gets better d-max.
We both know that it depends also a lot on the quality of the paper thats used - but with the right paper there will be a remarkable inkrease in density on the final print.

[Michael Mutmansky]

Ok, I see what you are saying, and it is (as expected) a more correct way of saying what I was trying to say.

BTW, I agree that the paper is often the biggest variable in this. The right paper can make a huge impact on the results.

[Craig Alan Huber]

Of course, now is when I wish I had paid more attention to high-school chemistry :-)

With egg-on-face (or should I eat some crow?) I admit I was only counting the Pd salt in the % solution, not adding in the NaCl as Kerik pointed out. Kerik - I am verifying off-line with Dick Sullivan, as you suggest.

Also many thanks to Michael and Harald for detailed descriptions of the chemistry and some practicalities of usage involved. At least in this case I am holding the paper as a constant (COT320) for a series of images. Coating with a 2" Richeson brush and 48 drops total solution over an 11x14 inch area I am getting nice results with a single coat.

Craig

[Craig Alan Huber]

And now, of course a new (but related) question: will I be able to use ordinary table salt for this mix, or will some lab grade be required? I assume I would want non-iodized salt. I went to the store recently to look, and was amazed at the number of salt products (over 10, not counting seasoned-varieties!)

Thanks,
Craig

[clay harmon]

Craig,

I use uniodized Morton's salt and have no problems.

[Michael Mutmansky]

Same here, but I prefer ammnoium chloride, so I started using that over the Morton's.