The whole point of the patent you mentioned is to convert the silver salts to silver iodide with a developing agent, then expose the paper and fix. There are other, more simpler ways to do this.

I started with some Kodak Polycontrast paper which has an expiration date of 1967 and soaked the paper in a 10% solution of potassium nitrate for about 5 minutes with a safelight. Hung up to dry in the dark, then exposed like POP. The exposed paper was then fixed in a 5% solution of plain hypo for about 10 minutes, washed, and dried.

The exposed paper had a pinkish brown tone, but when I placed it in the fixer the color changed to a nice brown tone. The pinkish brown tone returned when the paper was dry. There was a slight loss in print density while in the fixer.

I also toned some of the prints with a 10% KRST. The color of the print first turned to a slate grey color after a couple of minutes, but this color slowly evolved into a nice brown color after about 10 minutes. The KRST improved the color of the print so much that, at least with this paper, this will be part of the procedure.

Some notes and observations -

1. Lars Mellberg suggested using the potassium nitrate bath for converting DOP to POP. He is a very knowledgeable person who is very happy to share what he knows. Thank you Lars.

2. I tried exposing just the plain paper with no prebath. This works, but you need a lot more exposure the potassium nitrate seems to make the paper more sensitive.

3. There are a lot of variables when using old, out of date paper. The paper itself and how the paper was stored will both have an effect on the result you will get. Part of the fun is that you never know what you'll get until you try, and part of the fun is when you start out with old, out of date paper and you end up with prints worthy of putting up on the wall (or exchanging in an APUG print exchange)!