What is a pincloth? I'd like to tell you definitively, but I can only say, "I'm not sure." There are 9 pre-1785 references in the Old Bailey records, with the first appearing in 1754. Unfortunately, they don't give any description of what the pincloths looked like other than to describe the fabric. Kannik's Korner sells a pincloth pattern (scroll down) that is based off of the 1789 "Instructions for Cutting Out Apparel for the Poor." I've searched and searched for images dated during or just before the Revolutionary War, but they are like hen's teeth. Paul Sandby drew a couple that I found from 1759, but their sketchiness makes it hard to tell just what the garment looked like.
Detail - "London Cries - Fishmonger" by Paul Sandby, 1759, Yale Center for British Art