'Reactive slip' is something I have always been intrigued by! It is a coloured slip that will melt/vitrify just enough to react with any glaze put over it to yield unpredictable and (sometimes!) beautiful results. I was lucky enough to be given a sample to practice with and achieved some interesting (!) results. I think the most successful was using the reactive slip underneath a matt white stoneware glaze which produced a lovely mix of pale blue, greys and greens all dampened into pastel tones by the white glaze (seen on the 2 jugs).
The tall black vase is exactly the same slip underneath a clear glaze!! That is just how crazy the world of reactive slip can be.
Unfortunately, the recipe for the slip was a closely guarded secret and there is no more left for me to play with! For now, reactive slip you are free to leave the potting shed!