Regardless of cultural origin, any piece 18th century or older that has been fired to above 500°C with clay containing sufficient quantities of TL minerals (quartz and/or feldspar crystals) and radioactive inclusions (normally uranium, thorium and a radioactive form of potassium) can be tested.
Our quoted accuracy of ±20% can determine whether an object has been fired in antiquity or modern times thereby establishing its authenticity. Under ideal conditions, archaeological sites can be dated with a precision of ±6% if they are monitored for environmental radiation and wetness by leaving sensitive detectors in situ for a year. This is obviously not the case with the pieces we test where the dating conditions are far from ideal. Additionally, the restrictions on sample size for art objects limits the number of measurements that can be made.
Authenticity aims to distinguish between an original and a modern copy. Dating aims to provide a precise historical date to an object. TL testing can only date an object if it has been excavated under controlled conditions and we have been able to monitor the burial site in situ. If a large number of fragments in each location is dated, a mean value for that location can be computed. In this case the quoted accuracy would be ±6%. In typical cases when pieces have reached the art market too much information has been lost and the quoted age limits cannot be realistically better than ±20%. In most cases this is sufficient to determine authenticity.
Samples are processed and results issued within 4 to 5 weeks. In some cases, we are also able to offer 5 and 10 (laboratory working) days urgent services for an additional fee.
For earthenware pieces, samples of at least 50 mg are obtained in powder form from inconspicuous areas on the object by using a hand-held drill fitted with a tungsten carbide dental bit. The number of samples taken is dependent upon the size, configuration and condition of the piece. In some cases several samples may be required.
For high-fired pieces such as stoneware and porcelain, sampling is done using a diamond core drill bit approximately 4 mm in diameter. Two samples 5 mm in length are required, and are usually removed from the base or other unglazed areas on the object.
Bronze pieces that contain casting core can be TL tested. Bronzes are often cast around a clay mold and this casting core is trapped inside otherwise hollow sections, such as handles, legs, heads and torsos. Once this core has been extracted through the bronze outer casing, the sample can be dated in the same way as other powder samples.
Any object made of organic material such as wood, bone, textile, paper, shell, ivory and lacquer can be tested.
Ideally, samples should yield about 2 mg of carbon after processing, and the corresponding amounts of sample material to be taken are typically as follows:
Samples are processed and results available within an average of 6 weeks.
Most types of stones that are at least 300 years old are acceptable for analysis.
A sample of at least 5mm from the carved surface which includes “healthy” interior stone for cross sectional study is required.
Samples are processed and results available in an average 4 to 5 weeks.
Bronze, brass, iron, silver and gold objects that are at least 300 years old can be considered for analysis.
A sample of at least 5mm with surface patina and “healthy” inner metal is required, usually taken utilizing a small diamond disc.
Samples are processed and results available in an average of 4 to 5 weeks.
Most kinds of material can be CT scanned or X-rayed. However, the size of the gantry opening of 70cm on the CT machine limits the size of objects that can be scanned.
The images are analyzed and a report issued within 4 to 5 weeks.
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