In the first recipe, the zircopax may be the cause of the cutlery marking. Search zircopax on digitalfire.com and you will see more info on this. I would try a line blend of the glaze, reducing the zircopax to see how much is necessary to opacifiy your glaze. Then I would add silica in 5% increments to see how much the glaze could take before adverse effects arise. Also the first recipe that Min posted is a glaze I am testing right now. The matte surface of that glaze has an opacifying effect on its own, requiring less tin or zircopax to achieve the same opacity of your current white.