Walnut will indeed spalt, usually with white lines in the dark wood. When there is enough of it to cause the color changes, the boundries are usually filled with various colors in the darker schemes of walnut. I could be totally off guard with this, but I believe you have a wonderful piece of peach trunk wood there. Regardless what the wood is, you most assuredly found a treasure and did a great job with it. The Grand-daughter ain't half bad herself. I know your proud.
Working flat so I can play round,
Repentance Is The