After 17 years of providing dry powder and ferric oxalate solutions, we've gained some considerable experience in the matter. Here are some comments.
We at B&S have opted to provide a consistent base ingredient rather than try to provide a universal "witches brew" FO. Each addition to the product alters its characteristics, making some folks happy and others not. We have found that the product as it stands is suitable for most casual and beginning workers. The more advanced folks will probably have their own mix of eye of newt and toe of the frog.
One of the main differences found in FO is in the amount of free oxalic acid and free ferrous oxalate. More of either will increase the speed and curve characteristics. Liquid FO ages, building up some ferrous as it goes and increases in speed. Also the traditional ferricyanide measuring system is useful only in telling you whether the stuff is dead or alive. I had a FO test kit on the market in the early 80's that I abandoned due to the fact that it could not be fine tuned to any degree that was useful beyond doing a fog test.
Periodically, maybe once a year, we get this scenario: Class gets brand new kits for printing. Teacher makes a print with her negative and gets a very faint image. Teacher makes a print with her ferric oxalate that she brings from home and gets a "good" image. Teacher calls B&S and complains. Teacher says that new stuff isn't any good, etc etc. What has happened is that the teachers FO is 3 months old and has picked up some speed. I've been told by those with more sensitometry experience than I, that foggy FO may actually increase in contrast due to the fact that one can add more contrasting ingredients, but that the separation in the mid tones decreases. By foggy we are talking about incipient fog buildup, a fog that won't make a gray in the highlights but is there nonetheless, much like the old trick of fogging paper to lower its contrast. Astronomical glass plates were fogged to increase their speed.
I make the traditional ferric oxalate and dry it down, but it is precipitated out, washed and dried. I did the complete Harry Smith Portfolio in 1980 using home made liquid grade, before I developed the new method, so I have some experience with it as well.
I have printers who say they can calibrate with the powdered FO. Several years ago my friend Dick Arentz called and said his FO was bad, so I replaced it. He called and said that the new stuff was bad as well. We went around and around for a few days trying this and that. I asked how he knew it was bad, and he said he had to dial in less units to get it to print right. It was getting faster! I asked "What units?" he said the units on the dial on his plate maker. I asked how it measured the light, and he said there was a sensor in the thing. Long story short, replace sensor with a new one, and his exposures were back on the dime.
Dick mentored with Phil Davis, Phil unlike God who has only nine zones, has twenty one. Dick is very sensitometrically oriented printer, and has written and excellent book on the sensitometry of platinum printing. Dick always makes up fresh FO for each printing session from powder. In this way he is always at a known point and can predict very closely his print times.
Another issue is the use of hydrogen peroxide. H2O2 will reduce the ferrous in liquid grades and will prolong its life. This may be a good thing to add.... BUT! I did it for a long while without any problems until a 100 ml bottle exploded in my darkroom leaving nasty shards of brown glass stuck in the plaster walls. We now use the expensive cone caps in all of our small glass bottles as they are suppose to vent nicely. But, you know what? I am not putting any peroxide into any FO I ship to people, cone caps or not.
Hydrogen peroxide is used by a number of printers as a contrast control ingredient. If we add any, then the phone rings of the hook because their calibrations are offset.
Lead mercury and cadmium are also additions that can be made and according to OSHA regs, does not have to be reported if less than 1% percent of the product for some, and if less than .1% you can put anything in without reporting it on the MSDS. Typically these compounds are effective in .1 gm per 100 ml. Even if allowed to do so, I don't feel ethical putting lead or mercury compounds into the mix that is sent to the general buyer. Plenty of advance printers do use these compounds, and I custom mix liquid from powder with lead citrate in it for several customers. On occasion I've made mercury and cadmium mixes, but those customers have died off.<<g>
Like I say we have opted to produce a highly consistent powder that gives everyone a measured starting point. I probably have had more direct experience and user feedback on FO for platinum and palladium printing than anyone. I just thought I'd pass a brief summary to the List.
Dick Sullivan
<center>
Bostick & Sullivan
Http://www.bostick-sullivan.com
505-474-0890 FAX 505-474-2857
</center>
</x-rich>