I love my local public library. I found a book there called A Dictionary of Colonial American Printers' Ornaments & Illustrations and I've been poring over it for days.
All of the ornaments and illustrations in the book are relief prints produced in the American colonies from 1639 through 1773. As I looked through the book I noticed what seems to be a convention in depicting clouds, especially clouds that reveal some sort of apparition or miraculous event. The clouds are kind of round and puffy.
I decided to make the clouds in this print round too, but rather than carving concentric circles to define the roundness I wanted to make the clouds round in a moku hanga sort of way, just using color. Here's my version of round clouds: