The term "unseasoned" refers to wood that has been freshly felled or preserved by storing it in a water-filled trough or pond to maintain its naturally high moisture content.
This wood is much softer than seasoned timber and is therefore much easier to shape with hand tools.
To enhance the effect of the shrinkage, a half of a joint may be forcibly over-dried in a simple kiln while its encapsulating component is left green.
The components tighten against each other as the parts exchange moisture and approach equilibrium with the surrounding environment.
The swelling of the dry tenon inside the shrinking “green” mortise makes for an incredibly tight and permanent joint despite a lack of adhesives.