This previously unrecorded work was painted circa 1905. It is characteristic of works of this period in that the face and arms are more tightly worked while the handling of the clothing and background has become loosely painted. This lively technique is described further by Emilia Cardona: "Boldini was the dynamic painter par excellence. Dynamic not only because he was obsessed with rendering that which is alive and changing, but also because...he always wanted to surpass himself. Boldini was the painter of the gesture...In his paintings the gesture is weightless, it is movement, that is to say, transition; it expresses what it is, it contains what it has been, and it anticipates what it will become." Boldini rarely employed models for large scale portraits. The sitter was probably a prominent member of society and Mme. Paulette Howard-Johnston has suggested that she may be Mrs. Law, an American socialite, who was also painted by Helleu.

Boldini used the subject of a figure crossing the viewer's picture plane in two works from the 1890's, A Woman in Pink dress (1895) (also in the collection of Baron Maurice de Rothschild) and Mme. Hugo and her son (1898) (see lot 14) as with The Black Sash, these sitters do not appear to have posed for Boldini, but have unconsciously been caught entering the theatrical arena of his canvas. The influence of photography on Boldini is evident in these works.