In 1959 Alexander Calder (1898-1976) created a black metal mobile titled Rio Nero which collector Lionel Bauman purchased from the Perls Galleries, New York City (1967). Patricia Bauman received Rio Nero from her father's estate in 1989 and consigned the mobile to the Herbert Palmer Gallery in Los Angeles and L & R Entwistle and Co., Ltd. in London. The Greenberg Gallery, Saint Louis, Missouri, purchased the mobile for $500,000 from L & R Entwistle in March 1990. The Barbara Mathes Gallery, New York; Donald Morris Gallery, Inc., Birmingham, Michigan; and John C. Stoller & Co., Minneapolis, Minnesota, each acquired a twenty-five percent share in the mobile from the Greenberg Gallery.
In May 1990, the gallery owners saw the mobile for the first time and noticed that the work neither hung properly nor moved in a manner consistent with other Calder mobiles. In December 1990, the owners asked Klaus Perls, the noted authority on Calder and the artist's primary dealer from 1955-1976, to authenticate the Rio Nero mobile. After Perls deemed the work a forgery, Patricia Bauman declined to reverse the sale and the four galleries instituted legal proceedings. The plaintiffs, Greenberg Gallery et al., contended that Patricia Bauman, or someone acting on her behalf, switched the original mobile with a forgery and then presented it to L & R Entwistle as a Calder mobile.
In April 1993, the case was tried without a jury in Washington, D. C. and the Federal District Court awarded judgment to the defendants, Patricia Bauman and L & R Entwistle. The judge presiding over the case, Judge Oberdorfer, ruled out the testimony of Klaus Perls and the plaintiffs subsequently appealed the case. In 1994, the Alexander and Louisa Calder Foundation declined to include the mobile in the catalogue raisonné on the artist. On appeal, judgment was not overturned.