Hi. I'm just going to copy what I replied to in the other thread.

I'd suggest any brush that isn't plastic based would be fine to clean the hearth. You don't want anything that will melt or leave behind something due to the high heats. You can get brass or stainless steel brushes from hardware stores easily. A hemp or natural fiber based brush would also be fine however might not be strong enough to remove anything that sticks to the bricks.