Degraded ferric oxalate effect

I have just completed the calibration process described by Mark Nelson for printing from digital negatives, in my case onto Arches Platine with the Ziatype process.
On this forum, I have just come across the potential problem of the short shelf life that Ferric Oxalate has.
I bought my kit from Bostick and Sullivan some months ago,and, after an initial trial, came back to it over the last two weeks.
If my ferric oxalate is old, what would be the effect seen when printing with it?
I appear to have a good tonal spread on printing test step tablets, but the prints are looking dark, with the highlights coloured to the point of quite deep yellow, despite lengthy washing after exposure. I am using no contrast agent and not humidifying the paper prior to exposure. The ambient humidity in my bathroom where I make the prints is pretty constant at 65-70, though on reflection I do store the paper in my computer room which may be a little drier but not much.
Could this be the ferric oxalate, or some other problem, perhaps.
Thanks

sounds to me like you are not getting complete clearing. There was a long thread about this a few weeks ago right here.

The Ziatype process uses Ammonium Ferric Oxalate rather than the traditional Ferric Oxalate used in the "classic" printing style. A yellow highlight, as Clay mentioned, is usually due to in-sufficient clearing.

Although, the Ziatype can produce a yellowish highlight if the paper lacks sufficient humidity to obtain a full print-out effect. It doesn't sound like this is the case, though, since you say you're getting fairly dark prints.

John, call Kevin or myself at 1-877-817-4320 if you're still having problems, and we'll do our best to figure out what's going on. If we can't solve your problems, we'll send out fresh chemistry or paper (on our dime). If you happen to live in the UK, we've got a VOIP line that forwards to our U.S. office: 0207 0784187

Good Luck,

Dana