Soot on White Graduation gown! How do I verbs it? Gown is white 100% polyester (no return type) Soot is from malfunctioning gas...

Gown is white 100% polyester (no return type)
Soot is from malfunctioning gas stove. Damage is REALLY BAD! I probably shouldnt have, but I rinsed it contained by lukewarm water and mild dish soap (didn't help). Please assistance. I am in the doghouse (and deservadly so!)Thanks.