Looks like it's already dull enough overall. You could try the acrylic paint technique I mentioned. Also, you could try taking a lit match to it in a few spots, make it look slightly burnt. Or put a few knicks in it like it fell down the generator shaft when Maul was cut in half.
I had one made of metal, and the person who made it put some thick wires in the end and made the ends even with the metal handle, then burnt them to look like they were cut by Obi Wans saber.
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