Niel,
In regard to your last post first: You still must wash a print after the second fix and toning regardless of whether you mix your toner with HCA or not. (Toner itself contains enough ammonium thiosulfate to require this wash). Do wash after toning, whether or not the prints were washed clean to start with. I second fix and tone in one session. The prints previously have been given the first fix, washed thoroughly and dried.
HCA helps the thiosulfate compounds wash out more quickly. In the old days, when people were not so concerned about dumping heavy metals (selenium) into the environment or water-treatment plants, mixing selenium toner with HCA was recommended to save time. This, however, necessitated dumping the toning bath after the capacity of the HCA was reached, long before the toner itself was exhausted. This resulted in a lot of active toner getting tossed, which today I feel is environmentally irresponsible.
A better solution is to mix the toner with water and follow it with a separate hypo-clearing bath. This allows one to use the toner to exhaustion before dumping it. You will find that a toning bath will outlast several hypo-clearing baths of the same volume. (The final step is to wash as usual. I wash for one hour at a higher temperature regardless of the fact that I use a hypo-clearing bath.)
An even better method (my preferred method) is to simply replenish the toning bath when toning times get too long. I have print toning baths of varying approximate dilutions that I have been using for years with no ill effects. This greatly reduces the amount of selenium one is dumping and is more economical to boot.
This above is for print toning baths, where the effect is visible. For toning your negatives, you will need a fairly fresh solution. As it gets older, you can simply add it to your print toning solution as part of the replenishing.
Now, on to toning negatives: To reduce the time and get maximum density change you will need a fairly strong dilution. 1:2 or 1:1 as mentioned above. Your 1:5 dilution seems a bit weak to me. I use 1:2 and tone for 5+ minutes. The object is to tone to completion to get the maximum density change. This answers your question regarding the cumulative effects of toning. There is a point where as much of the silver grains have been converted/coated by the selenium as possible, at which point toning stops. I've read somewhere that extended times can actually reduce density. I'm not sure if this is due to the ammonium thiosulfate in the solution of is an effect of the selenium redissolving into the solution. At any rate, after about five minutes in a rather strong solution, you can be assured of complete toning.
Selective toning is possible with cotton swabs, brushes or the like. I prefer applying the toner carefully to a dry negative. If there are fairly dense areas around the area you wish to selectively tone, any bleed-over can result in a denser "halo" around the toned area. The best situation is a dense area that needs intensifying surrounded by very much less dense areas.
Another caveat: If you develop in pyro, the toner will remove stain from the negative effectively negating the intensifying effect. I have heard that treating the toned negative in spent developer (much like the final aldaline bath) may restore the stain, but have never tried this myself. Hope this helps.
;^D)
