I suppose you folks are gathering black walnuts now

Clean the hulls off of them and clean them up good. Dust them heavy with a fungicide like Captan, or Banrot. Then store them in the bottom drawer of your refrigerator until Spring. If you put them in ziplock bags or something like that, then punch the bag full of holes so that the seeds can get some air. Dust them with fungicide again and plant them after everything thaws in the Spring.

I wouldn't use fungicides for this project.

[ The mother tree that they were collected from was a timber variety notorious for having purple heartwood.
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In my experience all walnuts have purple heartwood when green, and dry's to the familiar rich brown color.