I've just started enamelling and am having consistent failures with white enamel (but only white enamel). No matter how long or short I leave it in the kiln it comes out with a pitted/curdled look. I am using the recommended temperature 800C. See photo below. Other colours, as in the blue in the photo, work absolutely fine. The blue and the white both came from WG Ball, but I bought a white from somewhere else too and I'm having the same trouble with it. Any ideas?

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