Have you heard about using these pens for marking a quilt? My friend Kathy told me about them. They are fine point Gel Pens that are erasable and disappear with ironing. They are less than $6.00 for the three of them at Target.
The back of the package did warn that the markings would come back in freezing temperatures, though. Still, it all sounded too good to be true (how often do you freeze a quilt anyway?) and I wanted something just like this for my Storm at Sea that I am quilting on my domestic machine.
But, being the good engineer that I am, I figured this needed at least a little experiment. I started with this piece of unwashed fabric and marked it with the purple pen:

I had confirmed earlier that the markings would completely disappear with a quick touch of the iron but came back in their original form after just a few minutes in the freezer.
I always wash my quilts so this went right into the machine with a small load of laundry on delicate. This is what came out:

If you look closely, you just see the faintest trace of the markings. I cut it in half and put the left side into the freezer (still wet) and the other side in the dryer with the laundry. After the laundry was finished, the piece on the right also went into the freezer.
The markings were all gone at room temperature, but I wanted to see what the freezer would bring up.

I thought I could see the very faintest of marks on the piece that hadn’t been dried near the cut edge.

This doesn’t really concern me since I suspect that the ink will continue to fade with drying and ironing. I know that my quilts are rarely subjected to freezing temperatures but I figure that if you can see the markings when the fabric is cold, the ink is still there and could reappear (or be causing damage.) If I wasn’t planning on washing and drying a quilt and I wanted to know it would still be pristine in 20+ years, I would probably not use these pens.
But for me, they are worth the risk of at least a try on a quilt. The pen writes nicely on fabric. I hear they are available in white as well but they weren’t at my local Target when I checked. I’m going to get to work on the Storm at Sea today. Hopefully, the colors I have will show up on the purple fabric. Otherwise, I won’t get much done since I will be driving all around the DFW area trying to find the white pens . . .