I saw these things for sale in hardware stores in Switzerland and decided to make some for myself. The best wood to use is very sappy pine.
http://picasaweb.google.com/nutfool/InsideOutCandle?authkey=Gv1sRgCKH54bulyoycRA#
http://picasaweb.google.com/nutfool/InsideOutCandle?authkey=Gv1sRgCKH54bulyoycRA#