I built one of these chairs in a 4-day course I took with John Robinson at his shop north of Toronto in 2006. This type of Windsor chair is called a “Tall Sack Back Chair”.
The chair was finished using milk paint, hemp oil and wax. I purchased the milk paint from Homestead House in Toronto. I first brushed on 2 coats of “Kentucky Green” milk paint. When the milk paint dried, I rubbed on 4 coats of hemp oil (also purchased from Homestead House), waiting 1 day between coats for it to dry. When the last coat of hemp oil dried, I rubbed on a coat of bees wax and then buffed it out with a soft cotton rag.