Don't waste your time and money. Buy Retayne at your quilt shop, wash in hot water with the Retayne and you won't have to worry about future washings. The Retayne will set the dyes and if you use hot water then any future washing can be made at any temperature.
I own a quilt shop and this is the only recommendation I make for setting the dies in quilt fabrics.
OzarksGma