Keep in mind that while one of the 2 ink components in these pens dissipates with heat (such as the friction of the eraser), the other component does not. The thermal ink may be gone, but the gel base remains. Many people, both quilters and cross stitchers, have used these and later found those ghost lines, which appear as either a faint brown line, a light white line, or what appears to be a grease mark, depending on the fabric they are used on.