Cobalt oxide produces an evenly textured blue glaze (1-3%) which is more intense than the carbonate. Cobalt almost always produces blues, which may vary somewhat with glaze composition, high zinc glazes tending to give greenish blues (especially if titanium is present) and high magnesium glazes tending to produce lilac or pink hues. Cobalt is quite soluble in glazes, consequently it has little or no opacifying effect in the amounts normally used (rarely more than 1-2%). Cobalt is an active flux and it may be necessary to take this into account when using it in some glazes, as it may increase their fusibility quite considerably. Like other raw oxides (or carbonates) of copper, manganese and nickel, cobalt may cause blisters or bubbles in some glazes due to changing oxidation state during the firing cycle.