I have sorted and cleaned about 100 bricks that came out of an old fireplace chimney which went through Christian's bedroom at home. He will use them without mortar to create a hearth for the oldest fireplace in his farmhouse. After using a skill saw to cut some shorter for the sides, they will be set in a bonding thinset.
I cleaned twice as many as needed to select the nicest colors and fitting bricks. Using a stiff brush with a mixture of 1/4 C bleach, 1/4 C detergent, and 4 C wot water; they were scubbed two times.