I have always pre-shrunk fabrics before sewing - if they are going to be washed afterwards with regular home care methods. I my dressmaking endeavors over the years - I always did so, and emphasized that this is a real service to my customers.
When I handled the Authentic Pigment Sweatshirts, before transforming them into Creative Sweatshirt Jackets - feeling that they will be washed at home afterwards, I felt I wanted to get rid of the excess dye that seemed to crock off on the bed of my sewing machine. Washing them (though they didn't shrink) served to end that dye crocking problem.
A recent discussion on a chat list in which I participate has re-emphasized the wisdom of pre-shrinking fabrics. The horror stories of immediate and latent serious health effects of working on non-washed fabrics served to further emphasize this to me. A new industry friend - Pam Erny, who is a professional shirtmaker, offered the advice as you will read below, and has kindly given me permission to share it in this Wisdom Section of my Gallery. Thank you, Pam!
"From my experience in the fabric business, visiting mills and converters, I think there are at least 2 reasons why pre-washing fabrics is necessary.
1. To remove the sizing, excess dye, etc.
2. When fabric is milled/manufactured, it is pulled and stretched a few time before it ends up on the selling floor of fabric stores. This pulling and stretching is a consequence of getting it into sale-able form for the home sewing consumer. First, it is loomed, then it is rolled under tension onto tubes, then people called "converters" use and "double and rolling" machines to fold the fabric and roll it onto short bolt boards. During these processes, the fabric is rolled under considerable tension to make the rolls (and then the bolts), as tight as possible...to make them as compact as possible for ease of shipping and for other reasons. So...often it is necessary to wash fabrics before sewing to relax them...- and 'sometimes' that is why they "shrink"...they are merely relaxing back to their original loomed proportions. "