I've never worked with osage (it doesn't grow much in Europe), but I've ring chased several other wood species numerous times. I prefer to ring chase a properly dried stave. Green wood tends to tear out more easily, and my rasp clogs up when I try to use it on fresh wood. Dry wood just ring chases easier for me. However, I do sometimes remove the sapwood of black locust prior to drying. In that case I don't strictly ring chase, but just try to stay within a ring or two. The final ring chasing will be done after the wood has dried.
Remember that good daylight really helps when finding the rings.
To say that early wood does not mix with late wood is inaccurate at best. Some late wood rings can have barely discernable lunar rings while others can have lunar rings full of early wood. I find that statement puzzling. TBB I. Chapter I, Cutting and Seasoning Wood. One of the first pics in the book shows a perfect example.
I use TBB only as a reference, but a pretty good one in this instance. Perhaps on some level early and late wood don't mix, but from a practical standpoint they clearly do. I have not worked 300 staves, but I have worked my share. Early wood exists in greater or lesser degrees within every ring so far as my experience tells me. This stave not withstanding.
Slimbob, you are mixing up your terminology. Earlywood is not the same as wood vessels. It is biologically accurate in saying that earlywood and latewood don't mix. Think of it this way: a tree lays down wood as it grows. If it grows in spring, it lays down earlywood. If it grows in summer(/autumn), it lays down latewood. How can a tree mix the wood that was grown in spring with that what was grown in summer? It can't.
Instead, what you are pointing out is that you find
large wood vessels in the latewood as well, and not only in the earlywood. In the earlywood we do find most big wood vessels for water transport; that is why this earlywood is weaker than the latewood. But the latewood is not void of wood vessels. It just has fewer big vessels.
What you should have said is this:
Some late wood rings can have barely discernable lunar rings while others can have lunar rings full of large wood vessels.
Then you would be correct.
I don't have a scientific explanation for 'lunar rings'. I do see them as well (esp. in elm) and I agree that they are visible because of patterns of the wood vessels. I can imagine they may be in a high concentration of wood vessels, creating a small weakness in the latewood. Just don't call them earlywood.