TL Testing:

What is TL Testing?

Thermoluminescence or TL testing is a scientific method of determining the age of a particular ceramic by establishing when it was last fired.

When clay is fired, the electrons of the atoms are thrown off their nucleus. Over a period of time, the electrons gradually reattach themselves. Using sophisticated equipment and procedures, TL testers can determine how many electrons have reattached themselves and, as a result, determine the age of the ceramic.

Where the ceramic is soft enough - say, in the case of earthenware or low fired stoneware - a sample of grains from the artifact is taken by drilling a small hole in its body. A hole measuring 1/8 inch (approx 3mm) diameter x 1/4 inch (approx 6mm) depth will usually supply enough material for a test. In the case of high fired stoneware or porcelain, a diamond drill is used to take plugs from the body. Usually, two plugs measuring 1/4 inch (approx 6mm) diameter x 1/4 inch (approx 6mm) depth will be sufficient.

Which artifacts can be TL Tested?

Most earthenware can be tested, although some early white-colored pottery does not yield reliable results.

Most stoneware and porcelain can be tested. However, some pieces are potted in such a way that the drilling of the plugs required for testing is either not possible or would essentially ruin the piece, for example in the case of a thinly potted bowl.

Where does the TL Testing take place?

There are two laboratories which 33dynasties.com call on to undertake TL testing:

• The Oxford Authentication Laboratory in Oxfordshire, England
  
  
• Daybreak Labs in Connecticut near New Haven

Both are run by competent scientists and both will give accurate results.

How do the two laboratories compare?

Oxford Authentication Laboratory

The Oxford Authentication Laboratory charges $360 per piece for testing earthenware and low fired stoneware, and $500 per piece for testing high fired stoneware and porcelain. The cost for drilling the test sample by an Oxford representative in New York is $85 for the first sample and $35 for each subsequent sample. Drilling for stoneware will range from $100 if undertaken in New York, to $125 if the piece is sent to a specialist elsewhere in the US. If it is necessary to send the item for sampling outside of New York City, all shipping costs must be borne by the purchaser.

Including shipping fees, a test for earthenware or low fired stoneware is likely to cost in the region of $500, with a cost of $700 for high fired stoneware or porcelain.

As of July 1999, the Oxford Authentication Laboratory did not have a backlog for tests and was able to provide results within 2 weeks.

Daybreak Labs

Daybreak Labs charge $295 per piece for testing earthenware and low fired stoneware, and $475 per piece for testing high fired stoneware and porcelain. However, they make no additional charge for drilling the pieces, provided they are sent to them at the owner's expense.

Including shipping fees, a test for earthenware or low fired stoneware is likely to cost in the region of $325, with a cost of $525 for high fired stoneware or porcelain.

As of July 1999, Daybreak Labs were not up to date with their tests. Because of this, results might not be available for a month or longer.

Important Note: It is worth bearing in mind that the major auction houses will only acknowledge results from the Oxford Authentication Laboratory in their catalogs. If you are considering the resale of the item by auction, it is probably best to have the testing done in the UK.

Our Policy on TL Testing

33dynasties.com can conduct a TL test at a prospective buyer's behest on any previously untested ceramic that we offer for sale, under the following conditions:

• The buyer pays in advance the full cost of the piece, plus the cost of the test and any shipping costs.
  
  
• If the piece tests positive (ie. if the date of the piece corresponds with the date listed in our catalog) the buyer is obliged to purchase the piece and it will be shipped to the buyer.
  
  
• If the piece tests negative (ie. if the date of the piece does not correspond with the date listed in our catalog) we will assume the cost of the test, as well as all related costs, and the entire amount already paid by the prospective buyer will be refunded.

Related Services

If earthenware is tested it will have been drilled with one or more small holes. If high fired stoneware is tested there will have be two small holes in the body of the piece. Please refer to the section What is TL Testing? for full details of drilling procedures.

33dynasties.com can arrange to have these holes matched and filled by a highly skilled and reliable ceramic restorer who has done exceptional work for us in the past. Depending upon the condition of the piece, the cost for this service will range from approximately $40 to $200, to which we add a service charge of $20 to $40.

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phone: (212) 431-3187     fax: (212) 431 7530     email: info@33dynasties.com