We potters are well rounded group! (No sarcasm intended!!) What have I mastered? Very thought provoking topic... Let's just say, what have I enjoyed learning and doing... Sewing, natural childbirth, playing the flute and piccolo, creating stained glass, gardening. I no longer sew, but can when I need to; childbirth, three is enough; flute and piccolo, 6 years in school, 20 years in an community concert band; stained glass, 20 years but quit when the clay bug bit; gardening, not so much as my weedy garden shows. I'm very proud of my successful children. My son is a research scientist and holder of a 5-year NIH grant, oldest daughter worked in the seismic industry, sailed the seven seas and retired at 38, my youngest daughter teaches ninth grade earth and space science, recently returned from Iceland with her students. Raising children is much like working in clay - finding the correct balance between firm and gentle.
Celia, Yes, use your porcelain powdered clay, mix with water, allow to soak for a while and use a blender or immersion blender to incorporate. Sieving is a good idea. Thin with sodium silicate or not depending on the look you want to achieve. Be certain to match the cone requirement of both clays. As mentioned, the glaze colors are brighter over the porcelain slip than over stoneware.