RE: Ferric Oxalate or Ferric Ammonium Oxalate
Hi Sandy, I'm not familiar with the Ammonium salt since I use the Lithium salt. As far as I understand from Mike's practical instructions the Ammium salt and the AFO sensitizer is what you need to do Ware-Malde POP process. Let me highlight some information from Mike's article: (URL: http://www.mikeware.co.uk/mikeware/Platino-Palladiotype.html) "... The printing exposure range (logH) values in Table 2 indicate the effects of these controls. We do not recommend the addition of oxidising agents, such as potassium chlorate, potassium dichromate or hydrogen peroxide to the sensitizer, as employed in the traditional method for contrast control, because the effect of these is not to uniformly contract the tonal scale, but simply to truncate the high values. If humidity control seems too bothersome, then the most consistent results can be obtained at normal UK ambient RH (40-70%) by mixing the platinum and palladium solutions in the ratio of about 3:1, respectively; this sensitizer has a contrast and speed that are fairly constant over wide variations in humidity and it yields a long range of well-graduated neutral tones and a good Dmax..." Please note that the Pt is not the usual Potassium salt, it's the Ammonium salt. I think you can use the K salt if you like to (adjusting the solution strength so that molarity is the same). My understanding is that Mike doesn't like K salts because it may cause forming of Potassium Oxalate which is insoluble, therefore will cause a gritty sensitizer... But since the amnt. of KPt salt will be 1/3rd of what you need for pure Pt printing, the negative effect of using the Potassium salt may not be that pronounced -> worth to try in my opinion. As you can see Mike doesn't favor addition of oxidisers for contrast control. My experience with Ziatype (Li salt variant) is that addition of Ammonium Dichromate definitely increases the contrast of the emulsion and is a very effective contrast control tool - and it shows no graining, gradation / tones remain smooth... Anyway, I would suggest that you contact Mike directly for further and more detailed information. I'm sure he'll provide you the best advices you can possibly have ;) BTW, I don't think you strictly have to control the printout during the exposure, at least if you use the Li salt... Since Li is very hygroscopic, a fair amnt. of humidity will remain inside the coating even if it looks surface dry. I just follow the same drying protocol (5 minutes laying flat on the coating table + 5 to 10 minutes blowing cold air to the paper which is tacked to the wall - bent slightly so that air can circulate both in front and back of it for more uniform drying) to maintain consistency. %90 of the time I just start to clear the paper without further exposure - after exposing it for my SPT I mean... In other words, I'd say it's perfectly doable with a vacuum frame. Hope this helps! Best regards, Loris. ________________________________ From: Sandy King [mailto:sanking@clemson.edu] Sent: 03 Kasım 2006 Cuma 17:55 To: alt-photo-process-l@usask.ca Subject: RE: Ferric Oxalate or Ferric Ammonium Oxalate Loris, I have Palladium II Chloride powder on hand. Looking at Mike Ware's directions, it appears that I can prepare Ammonium Tetrachloropalladate(II) by mising ammonium chloride with palladum II chrloride. Would this be all I need, along with the FAO, to give Ware's POP method a try? In other words, can a basic sensitizer be made with just Ammonium Tetrachloropalladate(II) and Ammonium Ferric Oxalate, or do I need something else? Also Is it possible to control contrast with the Ware method with dichromate? I would rather do this than attempt to do so by varying RH? Sandy
|