
'F. R. L. . . . frill!' dates from between 1878 and 1879.
It refers to the threat by Frederick Richards Leyland (1832-1892), in a letter dated 17 July 1877, to horsewhip Whistler if he met Frances Leyland (1834-1910) again. 1

Horsewhip, Glasgow University Library

'F. R. L. . . . frill!', Ashmolean Museum
A related sketch, Horsewhip m0661 was drawn on the verso of a draft for a letter dated 4 January 1878. 2
However, it is possible, that, like 'F. R. L.' Frill - of Liverpool begins to be uncertain about the White House m0718 (which is on similar paper), it dates from 1879, during Whistler's bankruptcy proceedings.
It is fully catalogued in MacDonald 1995 (cat. rais.) [more] (cat. no. 719) where it was dated 'c.1879'.

'F. R. L. . . . frill!', Ashmolean Museum

Horsewhip, Glasgow University Library

'F. R. L.' Frill - of Liverpool begins to be uncertain about the White House,Ashmolean Museum
A horsewhip!

'F. R. L. . . . frill!', Ashmolean Museum

'F. R. L.' Frill - of Liverpool begins to be uncertain about the White House,Ashmolean Museum
The paper is identical to 'F. R. L.' Frill - of Liverpool begins to be uncertain about the White House m0718 and has a very pale greenish-grey tinge although it is less shiny on this side.
It was not exhibited in Whistler's lifetime.
1: GUW #02585.
2: [4 January 1878], GUW #05964.