Taking a sample
To quickly evaluate whether it may be possible to date a wooden item through tree-rings analysis it is simply required to identify whether it has the necessary number of rings. A tree-ring sequence must be of adequate length to be unique and thereby matched to a specific date; similar to how a finger print may be matched to a specific person. If you can count over 70 consecutive rings on the end-grain of a single timber it is possible to attempt dating your object by tree-ring analysis.
End-grain is identified as where the tree-rings may be observed at a 90° angle to the direction of growth when the tree was living. Different end-grain patterns of tree-rings will be evident depending upon which part of the trunk has been used (as can be seen below). The end-grain may be visible in various places. Recording the number of tree-ring widths from different areas of one object (i.e., a number of different samples from the same object) and additional information obtained by photography or tracing (where samples cannot be taken) can often help us to produce a more accurate average sequence for a single given piece of timber, and is therefore a recommended procedure to enhance the dating potential.
Tree Trunk in Cross Section revealing "End-grain".
Note 1. To assess whether a timber can be tree-ring dating it is important that the end-grain (as seen on a cross-section through the trunk of the tree) is clearly exposed - such as at the end of a sawn beam.
End-grain patterns can indicate the original position of the pith.
The importance of sapwood and bark in dating
Sapwood is a very important feature found in oak which should be recorded or sampled whenever it is present. Sapwood is found on the outer rings of oak nearest the bark, as opposed to the inner rings or heartwood rings. Sapwood represents the outer tree-rings within which are pores which transported sap and water when the tree was living. Sapwood is usually lighter in colour and is considerably weaker than heartwood and more susceptible to insect attack and rot; it will often be found to have broken away from the heartwood on old beams or it will become separated when sampling.
Although few cores retain sapwood which can be measured and included in a series sequence, it is often possible to count sapwood that has become detached from the ends of samples. Mature oak trees have an average number of sapwood rings, therefore even if the bark is not evident, sapwood enables a more precise date to be ascertained for when the tree was felled. If bark is present, even if it becomes detached, please send it with the sample. The presence of bark is relatively rare and it may allow us to date the felling of a timber to a particular season within a year. It is important to include any samples or information on the occurrence of sapwood and bark to help us better date your wood.
Professional sampling techniques
Coring enables the taking of a core sample from what may otherwise be inaccessible timbers, this service is only available through our specialist team and equipment. Core extraction holes are 15mm in diameter and are located as discreetly as possible. The holes do not affect the structural integrity of building timbers and often fit in with existing peg holes and knots and can be left open. However, where required, extraction holes may be made good and restoration techniques applied make them virtually invisible at the additional cost of £3.50 per core hole.
Coring a sample from a main ceiling beam
Using a different technique our team can also sample most living trees and date them with no detrimental effect to the life of the tree.
Other sampling techniques
All samples or other records of tree-rings should be taken at a 90° angle to the direction of growth at the end-grain; where you can clearly make out the individual rings and not where a knot or other growth effect disturbs the normal general ring pattern. The sample needs to contain as many consecutive rings as possible to enhance its potential to be dated. The maximum number of rings will be found between the pith (centre) and the bark (edge), and wherever both pith and bark are present these should be included in the sample.
Sawing a section
Timbers removed from a building at any time, for example during repairs, offer an extremely useful opportunity for timber sampling. Otherwise please normally only consider sawing a thin section for dating where the section will not affect the value or the structural integrity of the timber. A section 1 inch (25mm) wide is ideal; thinner sections can be used but they are prone to breaking, while thicker sections will simply increase any postage costs.
Note 2. All wood samples sent to us will normally be trimmed and sanded on one side by us to aid accurate ring-counting.
Note 3. You are only charged per item you wish dated, so if you choose to take photographs or tracings take as many as you need to ensure accuracy and increase the chance of us being able to provide you with the date of the wood.
Note 4. In all cases of sampling it is important to make a careful record of the location from which the samples have been taken, and also to clearly label all samples sent for analysis.
Photographs and tracings
In some cases items can be dated from a good quality close up picture of the area or a simple tracing of the rings where the rings are clearly exposed. Photographs should be taken with a 100 ASA black and white film, again at 90° to the surface. To help avoid reflection and bleaching it is normally recommended to use external lighting and avoid using a flash. Although this can be a specialist job, with a little practice you may achieve results where the individual rings can be made out sufficiently clearly.