Ash Glazes

Hi all, I wonder if anyone can help with a 'not so sticky' problem I've recently encountered: I've used ash glazes a few times in the past and decided to have another go at them as I now have access to a higher firing kiln than my own small (cone six) kiln. I've started with a very simple fifty fifty batch of china clay to ash and this produced some moderatly good results however, a few weeks after first using the glaze it seemed to undergo a change and now flakes off the bisque very easily. If I can manage to get the glazed pots into the kiln without too much loss of glaze the result when fired is a delightful 'crawled' finish that I really like. If I correct the glaze to help it stick to the pots by calcining some of the china clay, the crawling disapears (as might be expected) and the result is rather uninteresting. I've also had a go at adding some gum arabic to the mix but this seems to have no effect at all, the glaze still refuses to stick and still flakes off. Any ideas 'much appreciated. Andy