I tested those new gel pens and the following is what I learned today......
The writing/markings will return if your quilt gets cold, even though you have ironed it away - I just washed and dried mine to see if the writing disappeared - then I placed it in the freezer after washing it - and yes the writing/markings disappeared and did not show up when the quilt was put into the freezer after it had been washed and dried.
I haven't tried Batiks to see if it retains the gel pen color.