I have stripped the entire down stairs woodwork and two stair cases using a heat gun and Dad's Stripper all went fine. Now the problem I started on the doors upstairs. They have an original finish under many coats of paint. The heat gun and Dad's is only partially removing the original finish which look like a faux graining on the raised panel doors. I can get the paint off but there seems to be a base coat of something that does not come off with heat, stripper, mineral spirits. I thought it was milk paint at first not so sure now. The house interior was done in -1901.