Once removed from the furnace, the sample is monitored to determine the precise rate at which it combines with atmospheric moisture.

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Though it has only been established on bricks and tiles of up to 2,000 years of age, research is continuing to determine whether RHX can be accurately used on any fired-clay material, for example earthenware of up to 10,000 years of age.

The original work of Wilson and co-workers was undertaken on construction materials, bricks and tiles.

The RHX rate is largely insensitive to the ambient humidity because the RHX reaction occurs extremely slowly, and only minute amounts of water are required to feed it.

Sufficient water is available in virtually all terrestrial environments.

This weight increase provides an accurate measure of the extent of rehydroxylation.

The dating clock is provided by the experimental finding that the RHX reaction follows a precise kinetic law: the weight gain increases as the fourth root of the time which has elapsed since firing.

Transferring the method to ceramics has brought additional challenges but initial results have demonstrated that ceramics have the same “internal clock” as bricks. These studies have encountered issues with components within the ceramics causing either addition mass gain or additional mass loss during the RHX measurement process.

The quality of data generated by the Manchester and Edinburgh groups has been due to analysing fired-clay materials which do not contain these components.

An item with a registry mark or number could have been produced before (less likely as the design would not be protected), or after the date of the registry mark.

The number listed for each year in the table is the first number issued that year. If your number is higher, but less than the number for the next year, then your item had it's design registered during that year.

These components can be an intrinsic part of the object, for example materials added as temper, or compounds which have become incorporated into the object during use, for example organic residues, or compounds which have entered into the object during burial or conservation.