Claret first enters the etymological record as a British nickname for Bordeaux red in 1700, not too long before Mason & Dixon gets started. The slang would then have been sixty-some years in use when first appears in M&D on page 192, with Mason in an English pub called the George distracting himself from the death of former Astronomer Royal Bradley with a “spirited expedition into the Deserts of Idiocy,” “producing his Pipe, pouring Claret into his Cup, and reclining in his Chair,” as he settles in for a friendly discourse on the eleven days lost in the transition to the Gregorian calendar.
Claret reappears repeatedly throughout the book, mostly in the hands of Mason (who you will recall does favour the grape over the grain). On page 340, he toasts the completion of a section of their line-drawing “gesturing reluctantly with his Claret-Glass… more festive than he’s been for a while.” We find Mason “regarding” his Cup of Claret on page 478. Thoughtful Dixon has been paying attention to all that cup-gazing, and for Christmas on page 509 he gives Mason “a Claret Jug of silver, crafted in Philadelphia,” probably more worthy of long regarding.
Late in the book, with the line drawing done, Mason is in Ireland to observe the return Transit of Venus, and isn’t short of Claret there either. Page 721:
Lord Pennycomequick, the global-Communications Nabob, now approaches Mason upon the Lawn, carrying in Coat-Pockets the size of Saddles-Bags four bottles of the Cheap Claret ev’rywhere to be found here, thanks to enterprising Irishmen in Bordeaux. “In my family since the Second Charles,” he calls in greeting.
“Isn’t a hundred years consider’d old for Wine?” Mason having risen kickish this morning.
“Oh, but I meant the Coat?”
Having no commodious centenarian coat, I could carry only one bottle of this very cheap claret. My $9.50 Bordeaux red blend hails from Chateau Bellevue and I don’t love it. It’s dry, but pretty thin and boring.
Back on page 360, claret was described as the “favor’d stupefacient of the jump’d up tradesman.” This may not refer only to the cheap stuff. A ‘tradesman’ in the early 18th century referred to the class of people who made money by working, including clergyman and barristers as well as merchants and shopkeepers—some of whom apparently would have been richer than the gentry. Others I suppose, could only afford claret more like this one, good for a bit of jump’d up posing only.