Charlotte,
Preparing vintage blocks for quilts varies from person to person but rarely if ever includes washing the blocks. The textiles are very delicate, will shrink and the weave is not as tight as current quilting fabrics plus bleeding colors were a bigger problem in years past than today. I was given some depression era orphan blocks, lots of grandmother's flower gardens & a vintage top not long ago....passed down from my great grandmother and a great great aunt.
The fabrics you add to your precious blocks are completely up to you. Just today, I was at a quilt show that featured several quilts of vintage blocks recently put together in tops and quilted using reproduction fabrics to keep the look cohesive...now, that may alter the value but if that's not your main concern, it's an option. I suppose it really depends on the look of the original blocks and the overall design you're going for. For my own blocks, I'll be adding some vintage fabrics---the perfect match for repairs and additions. If I have to add some yardage, I'd also choose a muslin as you've mentioned since I have very busy prints in the blocks and muslin or plain feedsack would have been commonplace back in the 30s.
As far as machine quilting goes, I hope someone on the board has experience in this and some tips for you. Someday when I get to the blocks that have been handed down to me, I'll probably hand quilt since it's the method I'm most comfortable with.
Best of luck! I'm looking forward to seeing some photos of your treasures.
Last edited by retrogirl02; 03-31-2012 at 11:30 PM.