Yes I have used them. I get mine at a local art store because I can choose my own colors.
I have used them directly on fabric using one of the Cedar Canyon plates and that turned out great. I have also just rubbed them on freezer paper and brushed it on fabric to give the fabric a more appealing look. It made the orchids and flowers more realistic in color.
Just wash you quilt normally. However, my normal is more like using a quilt soap and not what I use with my clothes/
It is great that they form their own protective cover and all you have to do is remove it and they are just like new.