I'm This is the go to wash in our studio.
It was brought to my attention by Jess a few years back and I huffed and puffed when I first saw her use it, but I quickly came around after playing with it, and was floored after seeing results when it's used in conjunction with the stencils, Since then, we've seen it referenced by John Britt in his glaze books.
(2) tablespoons gerstly borate
(2) tablespoons masion stain
(1) cup water
I imagine that any masion stain or oxide can be used when mixing this up.
I use this instead of using an underglaze wash when layering on shino glazes.