Oh, by the way....
There is a product called SISTAN that can be used to help permanence of the image. There was AG Stab which doesn't seem to be available anymore and Adostab that is basically a replacement, according to FreeStyle.
This is NOT a toner. It doesn't change color at all. With AG Stab, I didn't notice the darkening of the image in the item description. Use this as the last step after wash and squeegee off the excess and let dry. What I understand is that an active ingredient in these products protect the silver from degrading. I've used it few times.
If image permanence is really an important concern, you may want to check into these as well. If you are printing something like a family portrait, it may be important that grand children can show their grand children what their parents looked like.