The sale will include more than 80 costumes, stage jewellery, headdresses, opera glasses and parasols worn by the singer during her 40-year career.
Dame Joan became a star overnight for her performance of Lucia di Lammamor at Covent Garden in 1959. She retired in 1990 and lives with her husband, the conductor Richard Bonynge, in Switzerland, where her costumes have gathered dust in the attic. "I just couldn't keep them in the house. They took up the whole loft and I couldn't bear to think of them being hidden away," she said yesterday at a reception at Sotheby's.
The costumes start at size 14 - at the outset of her career - and go upwards, although Sotheby's would not say where they finished. They include the bloodstained nightgown that Dame Joan wore in the Mad Scene in Act III in the 1959 production of Lucia, designed by Franco Zeffirelli, and which it is estimated may fetch £1,500 to £2,500.
Another Zeffirelli costume, an 1840s-style burgundy velvet gown, studded with paste rubies, worn by the diva when she played Violetta in La Traviata in 1960, is estimated at £1,000 to £1,500.