Surface dirt removal from an 18^th century portrait.

The removal of layers of dirt (including smoke damage, accumulated atmospheric pollution, nicotine, soot etc.) from paintings is carried out following careful tests to ensure that no damage is being done to the underlying layers of paint, glazes and varnishes. In some cases this may be all that is required to bring the image back to an acceptable level of visibility. 

The removal of layers of often dull and darkened varnish is considered and carried out even more carefully, given the potential for there to be artists glazes or tinted varnishes present.

Surface dirt removal test from an 18th century painted ceiling with water damage.

The removal of layers of overpaint (previous restorations) can be done following tests and examination. Some overpaint may look unsightly but could conceal large losses. This is why removing such layers is undertaken on a case by case basis. 

Varnish and/or overpaint removal are considered after close inspection (often involving UV light examination) and tests. In complex cases this may involve more technical photographic analysis and some laboratory work. 

The emphasis in these processes is to avoid ‘overcleaning’.