Pencil cause the glaze to resist?

I have a client whose plate came out of the kiln like this. She used regular pencil and painted over it with Mayco Stroke & Coat, it was glaze fired to cone 06. We use pencil all the time but have only seen this once or twice. Any way to fix this for her?

I have a client whose plate came out of the kiln like this. She used regular pencil and painted over it with Mayco Stroke & Coat, it was glaze fired to cone 06. We use pencil all the time but have only seen this once or twice. Any way to fix this for her?