|Robe à la Française, 1760's|
|Robe a la Francaise, ca 1765|
|Robe à la Française, 1770-1790|
Not exactly plaid, but the pattern makes for a checkered look at a distance.
|Robe à l'Anglaise, 1784-87|
|Silk caraco jacket, 1770's|
I love this fashion plate and I live in hope that someone will make it one day.
|Journal des Dames et des Modes, 1797|
|François-Hubert Drouais, 1757|
|Princess Frederika Sophia Wilhelmina of Orange, nee Prussia by Johann Georg Ziesenis, 1768-1769|
Her apron is clearly plaid, but is her caraco jacket? I think it looks spotted, but some say plaid.
|Plucking the Turkey by Henry Walton, 1776|
|Young Moravian Girl. Johann Valentin Haidt|
|Oyster vendor after Mercier. Mezzotint|
|Portrait of a woman, unknown artist|
Tartan were around in the 18th century, and evidently not only used for kilts. An article on 17th and 18th century Scottish costume can be found here.
|Portrait of a Jacobite Lady by Cosmo Alexander, 1745-1750's|
|Flora McDonal by Allan Ramsey,|
|Sir Robert Dalrymple of Castleton, ca 1720|
|John Campbell by William Mosman, 1749|
|Dr. Sir Stuart Threipland, of Fingask|
|James and Alexander McDonald by William Blake|
|Prince Charles James Stuart by William Mosman, 1750|
|Woollen, twill-weave hard tartan man's coat, Scottish, 1740–50|
Click on link for a larger picture.