Silver nitrate added to clay body
Glaze additives aren't always appropriate for adding to a clay body, but sometimes they can be. I've never used silver nitrate or even heard of its use in glazes, but then I've never been a Raku artist. It sounds like a lot of fun, but I don't have the equipment or the community for doing it, so I've always stuck to plain mid-fire stoneware. 

If you have silver nitrate on hand, why not experiment with adding a small amount to your Raku body and see what happens. That's kind of the spirit of Raku anyway; experimentation. Raku (as I'm sure you're aware) isn't typically intended to be used other than as a beautiful object of art. It isn't even necessarily expected to be durable (at least not for decades). Since the kiln set-up is so casual, you probably aren't going to do any damage to your equipment. Just be sure to take the usual Raku precautions, maybe protect your kiln shelf with a disk of bisqued clay and wear appropriate clothing, gloves, eye covering, etc.