The following "Lost" item appeared in the thrice-weekly London Chronicle for 1761 (volume 9, no. 627, Feb 14 - Feb 17, 1761):
It is particularly worth noting that this notice makes reference to a white Newfoundland dog, which would indicate that if the dog were a Landseer Newf, it must have had relatively little black coloring.
Lost, on Thursday the 29th of January, a large white dog, of the Newfoundland kind; he has a large feathered and curled tail, and answers to the name of Lupo. Whoever brings him to the Duke of Richmond, Whitehall, shall receive Two Guineas reward. No greater reward will be given.
The "Duke of Richmond" at the time would have been Charles Lennox (1735 - 1806), 3rd Duke of Richmond, English military officer and an important political figure of the later 18th Century. Lennox was a noted patron of the arts as well, and owned works by George Stubbs, painter of one of the first great Newfoundland paintings.