The correct selection and sampling of suitable wood is
essential for accurate dating results.
The following has to be taken into consideration when sampling:
- Samples should not be taken from sections where the wood shows signs
of tension or compression (reaction) e.g. root or branch sections
- Single samples should have at least 80 annual rings.
- As many samples as possible should be available, should analyses of
one particular construction period be required. Only a well established
chronological series of annual ring patterns can guarantee exact crossdating.
To determine the date a tree was felled ("the cutting
year") the terminal ring of the last year of growth, must be there.
If the terminal ring is missing, but sapwood is still available, we can
estimate the "felling date" through experience. Adding the number
of missing rings is known as sapwood dating.
Sampling methods used in dendrochronological dating:
- Sampling using an increment
borer. A core sample of between 5 to 25 mm in diameter, according to
the type of bore used, is removed from the wood.
- Sampling using a magnifying measuring lens: the measurements of the
annual ring width pattern are taken directly from the sample. The annual
ring widths are then copied on a 1:1 scale onto transparent film, or
a blueprint is taken.
- The annual ring sequence of the sample is photographed and subsequent
measurements taken from the photographs.
- X-ray photography (computertomography) can be used for samples where
the annual ring sequence cannot be seen eg. in paintings or sculptures.