From the Christie's Web site; exposure increased. A genealogical sketch can be seen here, but Christie's Lot Notes provide good biographical information: "Martha, Countess of Lindsey, was the second daughter of William Cockayne (1561-1626), a prominent London merchant, and his wife, Mary Morris. The sitter's father, who served as Lord Mayor of London from 1619-20, accumulated a vast fortune by exporting cloth to the Baltic states on a considerable scale. Cockayne became an influential adviser to King James I, to whom he lent money, and who frequently consulted with him both in council and privately. He was buried on 12 December 1626 at St. Paul's Cathedral and the funeral sermon was delivered by the poet John Donne, Dean of St. Paul’s. Martha, along with her five sisters, received £10,000 on her father’s death.
In 1624 Martha married John Ramsay, 1st Earl of Holderness (c.1580-1626), the first favourite of James I after his accession to the throne in 1603. The marriage was childless and Holderness died on 28 February 1626. On 18 April 1627 she married, secondly, Bertie Montague, 2nd Earl of Lindsey (1607/8-1666), with whom she had five sons and three daughters. A Royalist army officer, Lindsey attended Charles I during his trial and was one of four peers to accompany the King's body to its grave at Windsor after his execution. Martha died in July 1641, aged thirty-six.
This portrait would appear to have been painted soon after her second marriage in 1627. The sitter’s beautifully observed dress can be dated to 1628-1631. The paned, ‘double-puff’ sleeve can be compared with that worn by Katherine, Duchess of Buckingham in Honthorst’s group portrait, painted in 1628, of The Duke of Buckingham and his Family (Royal Collection). The elaborate sleeve can also be seen in Cornelius Johnson’s portrait, painted in 1631, of Lady Margaret Hungerford (Iveagh Bequest, Kenwood House). The dress in the Kenwood picture can be further compared with that in the present portrait in the blue and gold ribbon bows and girdle.
The seemingly pointed inclusion of a single dead tree in the superbly rendered landscape behind the sitter may be a reference to the deaths of her father and first husband in 1626."