[alt-photo] Re: dilution of pt/pd

[Christina Anderson]

Loris,

Thanks for all this; it is VERY interesting to talk about moles vs. standard solutions. It makes much more mathematical sense, like comparing apples to apples.

The formulae I use were traditional formulae "on the books" so to speak, so I didn't come up with them, and I've used them for years (10 maybe?) to satisfaction. But how would I know how much precious metal I have been wasting?? Now I wonder if that bleeding I experienced with Platine might have been related to something entirely different than the paper and humidity.

 From what I am gathering, below, I am using twice as much metal as I need in comparison with the FO you are saying.  Put another way perhaps, I am not using enough FO to reduce the metal that I am coating on the paper, correct?  

Looks like you have taken into account the extra salt in the pd, did you also take into account the oxalic acid in the FO?

Yes I do care about the extra waste, and if you are certain that the ratio of moles should be 2 moles iron to 1 mole metal, then I have two choices it seems--to raise the amount of FO I use at time of coating or mix a weaker PD. Now that should save some $$.

Interesting, too, that even though my PT is referred to as a "20%" (10/50) it is actually only 15%.

BTW the gum literature is rampant with this confusion in the mixing of dichromates and gums.  A formula will be called a 20% when it is a 10+50, gum was mixed "2 in 5", Demachy used gum "twice this strong" (does that mean "4 in 5" or "3 in 5"???) and I would get so confused until finally one old book brought out this scientific inconsistency and just said, oh well. But with expensive metals if there is waste that is a different story.

Wish I was home in my dimroom pulling my step wedges out but that will have to wait (gasp) a month.

Chris

PS the old pt/pd formulae used 2 extra drops of noble metal per coating often, just to make sure there were enough...

Christina Z. Anderson
christinaZanderson.com

On Jul 22, 2010, at 5:31 PM, Loris Medici wrote:

> Dear Christina, just for an example of using molar notation, wherever appropriate:
> 
> PD (as you state) is actually PdCl2, or maybe PdCl2.2H2O (means it's hydrated with 2 water molecules.) I'll assume that what you have on hands is the former...
> 
> 1 mole PdCl2 = 177.33g (See this address: http://environmentalchemistry.com/yogi/reference/molar.html. There are many more in the web, therefore it's easy to find out this information - as long as you know the chemical formula of the compound in question...)
> 
> Molarity is weight of compound (g) in 1000ml solvent.
> 
> Therefore, the Pd solution you prepare is:
> 5g PdCl2 / 55ml water (actual figues) * 1000ml / 177.33g (to find molarity) ~= 0.51M (rounded)
> (1 mole PdCl2 + 2 mole salt makes 1 mole double salt of Pd, therefore the molarity of PdCl2 is equal to the resulting molarity of Na2PdCl4 in your example; PdCl2 + 2NaCl -> Na2PdCl4)
> 
> In Pt/Pd printing, according to the reaction formula, you need 2 moles of iron per 1 mole of noble metal. (Won't get into the specifics of this; it's well documented in many places - such as Mike Ware's wonderful site full of extremely useful information: http://www.mikeware.co.uk/mikeware/Iron-based_Processes.html) Therefore, your iron solution should be 0.51M * 2 = 1.02M (rounded)
> 
> The chemical formula for ferric oxalate is Fe2(C2O4)3.5H2O - as stated by B&S, and it makes perfect sense to use their formula if you purchase your FO from them, indeed. (See: http://www.bostick-sullivan.com/articles/ferriccoalate.html) OTOH, please mind that with FO, the composition may change from batch to batch and/or supplier to supplier. That's why Mike Ware calls it an "ill defined compound" - you can't be sure when it comes to FO... Anyway, let's assume we're in the ballpark:
> 
> 1 mole of Fe2(C2O4)3.5H2O = 465.829g (See the address above to check...)
> 
> 15g FO to make 55ml = 15g / 55ml = 27.27% = 270g in 1000ml, therefore, your FO solution is 272.7g / 465.829g ~= 0.58M
> 
> Now, there's something seriously wrong here; we should have come to something near to 1.02M for the iron solution - assuming: (a.) The formulae aren't correct and/or (b.) Your mixing instructions below don't mean "add water to make" but "add x into y ml water" instead and/or (c.) The B&S stated formula for FO isn't correct.
> 
> Using 0.58M FO for 0.51M Pd means that you actually will never be able to use up all the Pd you have put on the paper, because you don't have enough (molar equivalent) Fe in the coating solution. (0.58 < 1.02, considerably.) Eventually it also means that you'll wash more Pd (than what's needed) down the drain...
> 
> BTW, the strength of your Na2PdCl4 solution is: 0.51M * 294.21g (molar mass) / 1000ml (according to the definition of molarity) = 15%. In other words; less than Terry's 20% - which means he is actually washing more of the precious metal down the drain, relatively - especially so if he indeed uses 20% FO (< your 27%) as he stated in his last message...
> 
> You may not care for the extra wastage if you're getting good "pictures", or you may care - that's up to you.
> 
> It's very late now, and I'm sure someone will correct me if I'm making an "doubleplushorrible" mistake here...
> 
> Regards,
> Loris.
> 
> 
> 22.07.2010 20:51, Christina Anderson yazmış:
>> ...
>> Next question though, as Terry/Loris' discussion has called to mind percentages.
>> 
>> My standard PT is 10g/50ml
>> My standard PD is 5g/3.5g sodium chloride/55ml
>> My standard ferric is 15g/1g oxalic acid/55ml
>> My Na2 Sodium Chloroplatinate I get from B&S, as a 20% and mix it to 5%.
>> 
>> So I am not using a 20% palladium. Do you all use 20% palladium as does Terry?
> ...
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