I agree with Barb. Choose the block which is the most stained. (I would baste around the outer edges to hold layers together.) Give it a good soak and then gentle washing. Rinse out well and air dry. If it works, great. Assemble the quilt then wash it gently. If it doesn't work, assemble it anyway. Then wash it and give it a gentle tea dye. Remember it's supposed to look old -- it's old.