I was told once that to be sure and use graphite pencils for fabric not real lead pencils. Or vice versa. I forgot. I think lead pencils are banned. Anyway graphite is super teeny tiny powder particles that get into the fabric threads. That is what you are trying to get out, not an actual mark. It will take repetitive action like dowsing or erasing to get the particles free from the threads. I've had good luck with Mr. Clean Eraser.