We did not do this in our class, but this can add another wonderful layer to your surface of a bit of sheen or flux..... somethings I have tried in the past.
Bisqued pieces to cone 03
The wash was fired to cone 05
1 soda ash to 3 parts water (stronger more fluxing action)
1 soda ash to 6 parts water (weaker)
1 lithium carb to 4 parts water
1 borax to 4 parts water