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Treating a clay ground 'Hadra' water-jar (hydria), attributed to the Dromeus Painter
Artefacts retrieved from excavation are often covered in burial deposits. Removing these deposits can reveal the shape or decorative surface of an artefact. Burial deposits vary depending on the nature of the conditions on the site. The white deposit seen on this water-jar (hydria) is known as an insoluble salt incrustation. During burial, insoluble salts from the surrounding soil can bond closely to the ceramic surface making them difficult to remove.
There are two processes for removing insoluble salt incrustations from ceramic: mechanical cleaning or the use of chemicals. Mechanical cleaning, using fine tools under magnification, is a long process. Chemical treatments, involving, for example, application of dilute acids, is quicker but can be aggressive and require wetting the object to wash away unwanted chemical residues. Either process can cause damage to, or loss of, an object's surface if not carried out by a trained conservator.
The black decoration on the water-jar is not greatly obscured by the incrustations. It is suspected that the vessel had been selectively cleaned to reveal areas of decoration prior to its acquisition at The British Museum. Either chemical or mechanical cleaning (or both) may have been used to dislodge the disfiguring white deposit.
The remaining incrustation on the jar is not extensive, and no further cleaning of the vessel was carried out.