steam will certainly shrink your cottons if you do not pre-wash...anytime you want every thing to fit together and shrink together they should be pre-washed, toss in the dryer, then press...it has nothing to do with starch it has to do with the heat. some people never pre-wash and they like the 'shrunk' end product, but seldom will 2 different fabrics shrink uniformly...and i don't know about you but it is very normal for me to use 100 or more different fabrics in one queen size quilt...that could mean lots of different shrinking going on. i tend to get home from purchasing fabric, entering the house through the garage, the washer and dryer are first thing...and the fabric goes right into the washer before ever getting close to the sewing room. when i have alot to wash (like 25 fat quarters or something like that i set up the ironing board at a sitting height, put in a movie and sit and iron for an afternoon..it is as relaxing as hand sewing can be ;)