Detail of a rare Yeso surtout, no. 1170, designed 1930. 13¼  in (33.5  cm) high; 20½  in (52.1  cm) long. Estimate £30,000-50,000. This lot is offered in Lalique on 15 May at

Collecting Guide: Lalique

Ahead of the largest René Lalique vase ever to be offered at auction, specialist Joy McCall answers seven key questions for prospective buyers of the French glassmaker’s exquisite pieces