A small amount of powder turns the epoxy black. Additionally, the addition of powder makes it easier to sand the epoxy after it cures. I use epoxy mixed with coffee grounds to fill small voids in wood shavings. Adding a small amount of graphite powder to the mixture will darken the fill from dark brown to jet black. However, . . . Sanding produces black dust that can smudge light woods and be difficult to remove. It works well for darker woods like walnut.