H719 Black and blue with silvery spots

glaze H719, vase
This glaze can be a little tricky, but when everything is OK it is very good. You must try out the right thickness, and know that it will run if too thick. It is opaque or half transparent, glossy or matt with silvery or (blue) black crystals. Make a lot of tests before you give it up! 1270oC with ½ hour at top temperature.
   
nepheline syenite 69,25
zinc oxide 5,77
wollastonite 11,51
magnesium carbonate 3,85
Albany slip (the real thing) 7,70
rutile 1,92
copper oxide 3,08
cobalt oxide 3,08
vanadium pentoxide 2,31