You will need to contact the owner's representative to arrange access.
In the case of this object this can be done by:
Writing to Mr James Carleton at Farrer & Co, 66 Lincolns Inn Fields, London, Wc2a 3lh
Reporting A Data Error:
Reporting An Access Error to the HMRC:
A sardonyx cameo with the bust of Minerva
Maker:  Maker Unknown
Description: 
A sardonyx cameo with the bust of Minerva, the gold mount and border enamelled black and white and set with an openwork row of emeralds - Italian, 17th century, the cameo perhaps added at a later date
ID:  78494