I finally got a found a few moments to mix up Steven Young's black inlay slip for incised bisque ware pulled from Ceramic Arts Daily, and give it a whirl. I have made a few changes to his recipe... instead of using XX Sagger fireclay, I did a 1:1 substitution using Glomax, a calcined kaolin. This was just to mess with something and possibly help with fit, but mostly it was just to mess with something.
I also decided to mess with the colorants, forgoing the recommended oxide additions and just add Best Black Maison Stain 6600. Steve's recipe added 16% oxides to the mix and I matched this in a 1:1 ratio as well.
Steve's process of using incised bisque for inlay seems to work very nicely. Simply paint on the slip. Roughly scrape off the majority of excess. Use a green 3M pad to knock off the most of the remainder, and finish by simply wiping with a damp sponge.
Easy... took all of 3 minutes the first time through.