This paper applies the principles of archaeological stratigraphy to interpret a series of complex changes to a portrait of Robert Sydney, 1st Earl of Leicester (1563-1626). Technical investigation during the conservation of the painting revealed a number of alterations, including the addition of a garter ribbon and jewel and changes to the costume. The changes were revealed during cleaning and X-radiography of the painting, and samples were taken to study the paint layers and characterize the pigments. Lead antimonate yellow was identified as a component of the paint applied in the alteration of the costume, indicating the costume was probably altered after 1650. Stratigraphic analysis of the paint samples suggested that all the alterations were part of a single phase, which involved the conversion of a portrait of completely different individual to that of the 1st Earl of Leicester. -- SCMRE