It's not about fresh or used fixer. My printing method involves 6 liters of freshly mixed Ilford Rapid Fixer 1:4 in which I fix from 10 to 16 20x24 FB prints within the hour and then discard on the spot. I expose all my prints and stack them in a box until I get 10 to 16. I then proceed to develop them one by one, and then fix them one by one. The fixer is always super fresh. (No it isn't, since you've exceeded the capacity for optimum permanence at print 11 ...)
I've had this staining issue quite regularly. And often on the very first prints, which were obviously fixed in the freshest possible fixer. FB or RC, all the same.
Some papers were washed for 5 minutes, some others for 30 minutes. Regardless. I really don't know how to fix this. So far, I realized I had to dip my prints slowly in the selenium. And wash them an extra bit before throwing them into the selenium. But it's never guaranteed. Thank God, the stains are always on the edges, never inside the print!
I also dont quite get this two-fix-bath method.
On one side, manufacturers warn against any extra time in the fixer since it's very bad. Especially if the fixer is getting exhausted. Hard to wash, they say.
And then on the other side, a two-bath method involving a fresh and an exhausted bath and an extra bath time is seen as good? Yes, since the second bath ensures complete fixation and since the first bath is not really "exhausted" in this scenario. It does, however, require longer wash times.
I understand the idea behind the two bath method but Im not doing this. Theres no way I'll let my fb prints sit extra time in the fixer. A freshly mixed solution involving a low amount of prints is the best way to go, IMO. To each his own, but two-bath fixing is not only used by the world's best printers, it is recommended by ALL manufacturers, including Ilford.
There are a couple of issues in your posts and the responses to them to address here:
First is the issue of two-bath fixing. Yes, you can use just one bath, but if you are halfway interested in getting the residual silver level in your prints as low as possible, then the capacity of a single bath is VERY small. Ilford says 10 8x10 prints per liter. With your six liters of fix, you'd better stick to just 10 20x24-inch prints if you are using just a single bath (since a 20x24= six 8x10s).
Even then, the last couple prints through the bath will have significantly more residual silver than the first ones. The fixer does not get rid of the silver in the print, it just converts it to a soluble form. The reactions are complex, but suffice it to say that as silver builds up in the fixing bath, its ability to convert silver to a water-soluble form diminishes rapidly; used fixer can only do a part of this job. A second bath stays very fresh as long as the capacity of the first is not exceeded, and finishes off this job splendidly. You could use two six-liter baths and get 40 20x24s through them before having to discard the first bath and replace it with the second... I think single bath fixing is not only inefficient, but also a waste of money and good chemistry.
Let's discuss the Ilford archival sequence a bit. Ilford's "short time in strong fixer" approach is based on a strategy of preventing fixer to fully permeate the fiber paper base. This requires the fix to be strong to do its job before it has a chance to soak through to the paper base. This latter takes about 60-90 seconds. If you do soak the paper completely, then you have to use a wash aid and wash longer to compensate. Since there are many who find the Ilford method questionable, and since results may be different with other papers than Ilford's, and since timing is, for me at least, a bit too critical for my work flow, I have decided to use my fixer 1+9, two-bath and use longer times (1.5-2 minutes in each bath) and the subsequent longer wash. I find this a much more economical use of fixer and my prints pass both residual silver and residual hypo tests with flying colors.
Now, on to staining in the toner. Two things generally cause staining: insufficient fixing or the prints being transferred from a too-acid environment into the toner.
Your 16th 20x24 through six liters of Rapid Fix at one minute or less is likely not fixed adequately enough to be toned without staining. Again, I'll advocate for two-bath fixing... but enough! Just stick to the 10 8x10s/liter capacity and you should have no problems with inadequate fixing.
Ilford Rapid Fix or Hypam 1+4 are too acid to transfer the print directly from the fixer to the toner without staining. I use the same fixer 1+9 and have no problems transferring directly from the fix to the toner. Others use an alkaline fixer or plain hypo for the second bath to accomplish the same thing, i.e., keeping the prints from being to acid when transferred to the toner.
If you use an acid fix, like you are, then you need to wash your prints fully before toning. The problem with an incomplete wash is that the wash doesn't act evenly over the print; there are areas that are more and less washed until "complete" washing is reached. A rather short wash may leave areas with lots of undissolved-out thiosulfate compounds in them. The toner will react differently in these areas than in the washed areas and the toning may be blotchy and uneven.
Staining in the toner can also be a result of manufacturing defects in the paper you are using. There was a thread on edge staining on some brands of paper in selenium toner here a while back. The more I look at your particular situation, the more I lean toward this answer. Print one through your fixer washed for 30 minutes should not stain... unless there is something wrong with the paper itself. What paper are you using?
One more thing can cause staining. Physical damage to the print can cause chemical changes and possible staining in the toner. Since your staining seems to be on the edges, maybe there is a problem either in the manufacturing (cutting the paper down to size) or in your handling of the paper when processing. Test with an undeveloped but fixed sheet, very carefully handled (or portion of a sheet with 20x24!) to see if it stains in the toner. If so, it is likely a manufacturing defect.
Best,
Doremus