Shrinkage
I measured hundreds of pieces of fabric before and after washing them - just to see what happens.
For all my quilting cottons - I now do the hot water soak for at least two hours - or until I remember to wash the fabrics - and then wash gently in cool to warm water and dry "until done" - I have a dryer setting that stops when "done".
I do put like colors together - so in case one is a bleeder, it won't make too much of a difference - and I'm not chancing ruining other colors.
From my experience - most of the fabrics shrank more in one direction than another. Very few of them had little or no shrinkage. I have had up to 2.5 inches of shrinkage on a 42 inch width of fabric (a Michael Miller black and some others) with no shrinkage on the length - I had over two inches shrinkage per yard in length on the Legacy muslin (which is a very nice muslin) from JoAnn's.
From what I have heard, fabric will also shrink when steam pressed - and I am going to go downstairs and check that out right now. I have some "virgin" legacy muslin on hand that I was going to use for another experiment, but this one will be quick and easy to do.