I too have a house built in 1850, and all the bedrooms have wide pine plank floors that have been painted many times. We were thinking of sanding them and refinishing them, and I thought to buy a lead test first. Good thing, because I am pregnant, and there is lead paint beneath the top coat of paint. We aren't sure what approach we will take now, but if you have children or women of child-bearing age in the house, be extra careful because before 1978, lead paint was used throughout homes, esp. on floors, trim, and windows.