When Ferric Oxalate Goes Bad - Pictures at 11:00

[Dan Williams]

I have some ferric oxalate for Pt/Pd printing that is approaching the dreaded 3-month expiration. Except for the days I have been using it, I have stored this in a brown bottle inside another brown bottle in my refrigerator. By the calander, I am about 2 weeks under 3 months. So far I am not aware of any change in its effectiveness. When this stuff is past its prime, how do I know it is time for a change?

Dan Williams

 

[Robert Hall]

When your process fails.

I have used FO up to 6 months with success.

I am now re-setting up the darkroom after a year (moving and building a new one) and will probably throw out the old.

 

[Joe Lipka]

My experience with bad FO is dull highlights (everything is grey) and weak shadows.

I mix up very small quantities and use it up quickly.

 

[photomc]

Just curious, Joe...how small a quantity - 5ml?

 

[Jorge]

I have used 8 months old FO with no problem. If you see dull highlights, an overall haze and it is hard to clear, then most likely it is time to make some new FO. Otherwise, use it!!!

 

[donbga]

Just curious, Joe...how small a quantity - 5ml?

5 ml? That's about enough for 5 8x10 prints.

 

[Joe Lipka]

I usually weigh out the FO into 3 brown glass dropper bottles and then add the hot water when I need to coat. I normally weigh out 2.79 grams to each little brown bottle. A day or so before I get ready to coat, I will add 10 ml of water to a bottle.

My drop count for an 8 x 10 print is 18 drops FO.

 

[scootermm]

5 ml? That's about enough for 5 8x10 prints.

um not sure... maybe Im going crazy but that seems like an awful lot.
my coating measurements for a 7x17 amply coated area is:
FO: 1.2mil
Metalsalts: 1.2mil

just an FYI
I did this at first and was coating entirely too much and started coming down in the quantities per many peoples suggestions (Kerik, Clay Harmon etc) and it works just as well.

 

[photomc]

I usually weigh out the FO into 3 brown glass dropper bottles and then add the hot water when I need to coat. I normally weigh out 2.79 grams to each little brown bottle. A day or so before I get ready to coat, I will add 10 ml of water to a bottle.

My drop count for an 8 x 10 print is 18 drops FO.

Thanks Joe, just wondering how small an amount people made up. 10ml sounds like an amount that would be good for the on and off times I get to print. And will not be letting anything go to waste, and not be running out either.

Matt, sounds like good advice. Last round I was using 4 drops of FO + 4 drops of metal salts per 4x5, 6+6 drops for 5x7 and 10+10 for 8x10. That is with Arches Platine, with Cranes Cover I found I had to up the drop count at least 2 drops of FO and 2 drops of metal salts per size.

 

[donbga]

um not sure... maybe Im going crazy but that seems like an awful lot.
my coating measurements for a 7x17 amply coated area is:
FO: 1.2mil
Metalsalts: 1.2mil

just an FYI
I did this at first and was coating entirely too much and started coming down in the quantities per many peoples suggestions (Kerik, Clay Harmon etc) and it works just as well.

I think the amount of FO used to coat a print depends on the method of coating, type of paper and whether or not platinum is used in the form of NA2 or just the non double salts of platinum for color.

Doing the math:

Using Joe Lipkas example of 18 drops of FO for an 8x10 inch print size works out to 0.9 ml of FO (one assumes that each drop is approximately 0.05 ml).
Using those quantites per print one could expect to coat 5 to 6 8x10 prints with 5 ml of FO. For the sake of simple math lets round that to 20 drops per 8x10 which yields 0.0125 ml per sq inch.

Using your figures of 1.2 ml of FO per 7x17, works out to about 0.0100 ml per sq. inch. A noticeble difference but not by an extreme amount.

Arentz reccomends 2.5 to 3 ml per 8x10 total amount of solution (FO + plt/pld Salt) (and also states that this qty can be reduced by 1/3 if using a coating rod). So assuming that one uses a coating rod to coat with, then using his minimum amount would be 0.8375 ml of FO or around the same qty that Joe is using.

The amount of coating could be further reduced if coating with a magic brush. Howver one difficulty crops up when a set ratio of FO+Metal Salt+NA2 is desired if one is measuring in drops to obtain a desired contrast or to prevent bronzing when printing with pure palladium. IOW, using a few more drops than minimally needed keeps these ratios easy to mix.

At any rate 18 to 20 drops of FO per 80 sq. inches may be a little heavy but not by too much.


It's been my experience that I'm a little happier using a tad too much than too little sensitizer and not producing a weak print.