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

[Terry King]

Loris


My objective is to produce platinum prints with good rich blacks, the optimum contrast range for the process and fine gradation.


My negatives are exposed and developed to achieve this. We have also developed a method of making digital negatives which is comparable.


The dilutions of 20% for the sodium tetrachloropaladate, potassium tetrachloroplatinate and ferric oxalate enable me to achieve prints which reflect the qualities of the negative .


The dilutions are the minimum amounts needed to avoid solarisation or reversal.


The method is very simple and it works.


Captain Abney once said ' The only advantage of this gentleman's formula is that it adds to the expense'.


My suspicion is that the only advantage of Mike Ware's methods and yours is that they add to the complication.


Terry








-----Original Message-----
From: Loris Medici <mail at loris.medici.name>
To: The alternative photographic processes mailing list <alt-photo-process-list at lists.altphotolist.org>
Sent: Thu, 22 Jul 2010 23:31
Subject: [alt-photo] Re: dilution of pt/pd


  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? 
... 
_______________________________________________ 
Alt-photo-process-list | http://altphotolist.org/listinfo