Quote Originally Posted by cliveh View Post
No, you should use neither. If you follow Talbot's original notes you will see this was not used with his salt prints. As soon as you use fixer with a salt print you destroy the original colour. What you need to do is take a large saucepan of water and bring it to the boil. At the same time you keep pouring in as much salt (NaCl common salt) as will dissolve. What you are making is a super saturation salt solution. When no more dissolves, you let the solution cool. Bottle this and after exposure of your salt print pour this over the image. This will stabilise the salt print, but not fix it (having said this, I and Talbot have noticed that if you get the proportion of salt ratio in balance with the silver nitrate solution coated on the paper, it will be quite permanent, but this is a different story we won’t go into here and one I can't do it consistently). You then need to scan it when dry before the image deteriorates.
This assumes, of course, that you're trying to simulate Fox Talbot's early work. Indeed, he did use NaCL early on but was unhappy with the results (he tried several methods to varying degrees of success). Herschel came up with Hypo (now known as Sodium Thiosulfate) as a means to permanently fix out the excess silver and passed the info on to Talbot (Herschel was very involved with many of the early chemical processes). Both Talbot and Daguerre switched to Hypo when it became clear that sodium chloride was not up to the task.

In answer to the OP. Sodium Thiosulfate is the fixer you want to use. As you've already noticed, Ammonium Thiosulfite is far too active for many of the older processes. Salt prints, Albumens, and VanDykes, all work best with plain Hypo. For VanDykes I use 1 heaping tablespoon of Hypo crystals to 1 quart of water. Works like a champ!