What needs improvement? The over 300 recipes do not have photos of test tiles associated with them. Artwork throughout the book in some places give the name of the glaze (ie: Copper Matt), however the name may not be explicit enough (ie: there are six copper matt recipes and many other copper matts not called "copper matt"). Some labels are incorrect (ie: "Vases" (Horsehair raku))--> these are actually two crackle vases and one horsehair raku vase. You could do without the personal statements of the invited artists. It is the wrong target audience for this type of book. It would be better to put additional techniques or photos of their work or them performing a technique that is visually aided.
Now the good! Even though there are no test tile photos, the comments are helpful (ie: requires heavy reduction or thin or thick coats). There is a good range of raku colors represented within the recipes and crackles, matts and glosses. There are a good range of construction techniques shown among the selected artists (ie: slab, wheel-thrown, wheel-altered, carved, sculpted, etc.) showing how these methods are best enhanced by raku glazes. There are also many glazing techniques (naked raku, slip resist, paper clay, etc.) that are interesting.
In all, the book is a good book and I would recommend it to others. I think a revision could make it an excellent book.