Totally agree with PaperPrincess!! I'll make scraps and test each. I test them to the limit ... hot water, hot iron, wash, soap, dryer, stitching through it (to make sure the marks don't transfer to the thread!). I try to test everything that my quilt might go through before it's done. Sometimes I'm testing multiple products for one quilt because (as an example in my navy and white quilt) my blue frixon pen will not show up on navy fabric, and my white sewline pencil will not show up on my white fabric.