I sent an email to F&P asking the same question. This is the answer they sent-I will give it a try.
Aug 10, 14:18
Here are some methods to help with getting the marks out:
1) Mix some SHOUT Ultra Gel with some water to make it smooth and then apply to pencil marks with a Q-Tip or small mascara brush. Gently rub and work it in. Air dry
overnight and NO marks from the solution or pencil marks are visible (or almost gone/not noticeable). This works on 100% cotton fabrics.
2) Mr. Clean eraser works well at getting the marks out also.
From the manufacturer:
The most common cause for this is that the pencil was not tested on the fabric before using or to much pressure was applied to make the mark.
We recommend testing because there are more sizings and finishes on fabrics today than ever before. These prevent dust and debris from penetrating the fibers.
When the marks penetrate the sizing, they are equally hard to remove. Therefore, testing is the best way to determine this and avoid problems.
Secondly, if you make the marks to dark, it makes it harder to remove them. If the marks are pressed over or even rubbed they go deeper in the fibers.
When a needle penetrates them, they also get under the thread and it is hard to reach them. Starching the fabric can also inhibit the marks. Starching over the marks
only coats them and you have to soak them; but, on the other hand, if you starch and then mark, it sometimes makes the marks easier to remove.
Soaking, erasing and brushing are all things that can help. It depends on the fabric type, the color of the fabric and how it was used.
When the marks are colors, it is certainly harder to remove them.