Her collection was, unlike many similar contemporary ones, well-curated. In 1766, the Genevan Romantic and philosopher Jean-Jacques Rousseau met Bentinck, admired her knowledge of botany, despite his opinion that women could not be scientific, and offered his services as her "herborist" (plant collector). She corresponded with Rousseau until she sent him a copy of Georg Rumpf's "Herbarium amboinense", a botany of Amboyna in what is now Indonesia, as he felt this opposed his ideal of free nature. The Portland Museum at Bulstrode was open to visitors, along with its zoo, aviary and vast botanic garden. Many came: scholars, philosophers, scientists and even royalty, and the collection became a "cause célèbre". Her fellow collector Horace Walpole commented on it:  or, in the words of Mrs Delany (a botanical artist and longtime friend):  Her collecting was also encouraged by her creative milieu: the Duchess and Delany were both members of The Bluestockings, a group of aristocratic women seeking increased intellectual opportunities for members of their sex. Her natural collection was the largest and most famous of its time, with few geographical bounds; it included objects from both Lapland and the South Seas (she patronised James Cook and bought shells from his second voyage through dealers). She drew and recorded its specimens, sorting them innovatively in type species and displaying them alongside ancient remains such as the Portland Vase, which she bought from Sir William Hamilton. Lightfoot later wrote in the introduction to the 1786 auction catalogue that it was her "intention to have had every unknown species in the three kingdoms of nature described and published to the world", but this was thwarted by Solander's death in 1783 and her own two years later. On her death, with her children uninterested in the collection, her son's political career to finance and her creditors' demands to be paid, it was her will that it be sold. The collection was entirely dissolved at an auction of over 4,000 lots at her Whitehall residence from 24 April to 3 July 1786. Hundreds of people attended, although some fine and decorative arts were bought back by her family at the auction, including the Portland Vase and pieces from a silver-gilt dessert service the Duchess had designed herself, crawling with exquisitely modelled insects. However, the vast majority went, including the whole natural history collection; Walpole records that only eight days included items other than "shells, ores, fossils, birds' eggs and natural history."