The re-fired ceramic is then weighed immediately, using a highly accurate microbalance, to determine precisely the rate of water recombination.Once the rate is known, the age of the artefact can be extrapolated.They calculated that the rate of reaction is independent of atmospheric moisture levels but is governed by the ambient temperature averaged over a ceramic’s lifetime.
This motif along with others, such as the fish scale and pipal leaf designs, continue to be employed into the later Kot Diji and Harappa Phases.
At present, the most widely used alternative technique is thermoluminescence, which involves measuring the amount of light given off by a sample because this is related to the dose of radiation an artefact has received across its lifetime.
One of the limitations is that it requires a lot of extra information about the archaeological site such as radiation levels, which may not be accessible if artefacts have already been sitting in a museum for many years.
They also tested a “mystery brick”, with the real age revealed to them only after their testing was completed — they got 340 years, and its known age was 339 to 344.
An interesting thing occurred when they tested their technique on a medieval brick from Canterbury: after repeated testing dated it at 66 years, they realized that the intense heat generated during a Second World War blitz had re-fired the brick and effectively reset its clock.