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.
Originally Posted by scootermm
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.