The theft occurred sometime between 8pm on Tuesday, October 11 and 8.15am on Wednesday, October 12 - the viewing day for a two-day sale on October 13-14. Police believe a burglar gained entry to the building, The Old Barn in Rodborough Common, using a ladder to reach a very small window, which was then smashed to gain access to a cabinet positioned close by.
Although the building was fitted with a security system, it appears the thief used knowledge of the position of sensors to access the display case without triggering an alarm.
The cabinet contained a number of the sale's potential highlights, including a bamboo libation cup c.1700 (estimate £3000-5000), a Qing jade brush washer in the form of a pomegranate (estimate £800-1200) and a 14in (35cm) Republic period blue and white porcelain figure of Guanyin holding a bottle vase (estimate £1500-2000).
The sale (the largest staged at Stroud Auction Rooms) went ahead with scene of crime officers still on site.
Anyone with information should contact Gloucestershire Police quoting reference 69/October 12 or call Crimestoppers on 0800 555 111.