Adding 10% GB may just make your glazes glossier and a bit more fluid. Here is a test tile I did using only GB as the flux. Going up increases in Kaolin and to the right increases in Silica. There's a certain point that you get some depth with 'boron clouding'. I remember it being related to how much silica is in the recipe too. Cone10.
Do you have any rutile/titanium/tin? Have you tried layering glazes?