This book gets two stars for the pretty pictures and author's experiments with coal ash.
I originally borrowed this book form my library hoping to troubleshoot an ash glaze that hadn't turned out as planned. This book did not help out with troubleshooting, or even give me any hints where to start. It may be useful if you are unable to search the internet for pictures of ash glazed ceramics or ash glaze recipes.
If you're looking for help with ash glazes gone awry, or using washed vs. unwashed ash, or any other information about ash glazes, I highly recommend saving your money and buying Robert Tichane's Ash Glazes.