Time capsules rarely attract more fanfare at their unveiling than their installation, but an unexpected one at London’s National Gallery certainly has. Constructors uncovered a letter entombed within one of two false concrete columns in the foyer of the Sainsbury Wing. The letter was written in 1990 by donor John Sainsbury (Sainsbury and his two brothers Simon and Timothy originally donated £40 million to the National Gallery for its extension) and snuck into the column during its installation. It details Sainsbury’s great disdain for the column, which he described as “a mistake of the architect” that the National Gallery would “live to regret”. Regret indeed, as more than 30 years on, the letter was discovered in the pillar’s demolition during the wing’s redevelopment, due to reopen in May next year. John Sainsbury died in 2022, but the 1990 letter makes clear how he would have felt. It reads: “Let it be known that one of the donors of this building is absolutely delighted that your generation has decided to dispense with the unnecessary column.” A gloriously petulant “I told you so” from beyond the grave.