A barrel stave, for example, can be made of wood with very narrow regular rings.Felling date and area of origin of wood from many archaeological finds of barrels has been successfully determined.
Wrap the sample in clingfilm to seal the water and prevent drying out.
If the wood is fragile, a thicker slice can be taken, so there is no danger of the material falling apart.
It is not a problem that the disc breaks - the parts can usually still be used.
When the disc is sawn, then look at the growth rings.
The best dendro-sample is at the place where the tree has grown regular, without distortion.
If bark or bark edge is preserved on the sample or object, the dating for the felling of the tree is accurately dated.