These four stages of natural aging on deadwood are from an article by François Jeker that appeared in Bonsai Today 103 (out of print). Francois is a accomplished bonsai artist (and deadwood master), gardener, author (Bonsai Aesthetics) and more.
Stage one
A freshly peeled branch or trunk will have completely smooth wood.
Stage two
Over the years, due to drying in the sun and wind, the wood will split into apical cracks (see below for more on apical growth and cracks).
Stage three
Much later, cracks that are perpendicular to the apical cracks will appear and form a “snakeskin” pattern.
Stage four
Continued exposure to harsh weather, fungal decay and xylophagous insects (insects that feed on woody plants) hollow the deadwood out in this final stage.
Apical growth
You can see signs of apical growth in veins and cracks that follow sap as it climbs from the roots to the tips of the branches.
Concentric growth
Concentric growth will first be visible in concentric hollows and healing calluses. You can also trace it in hollow trunks.
Coming together
Apical and concentric growth come together where branches grow off trunks. When this happens, interesting patterns are often formed.
very cool article – Thank you, Matt