Honeycomb firing tray getting carbon contamination, how to clean?

[belledent]

Hello all, I got some carbon contamination on my honeycomb firing tray in my Ivoclar oven. What is the best way to clean out that dark stain so future porcelain firing won't get the contamination? I tried steamer, bleach, baking soda....
Thanks for your help

 

[Affinity]

Buy a new one.