Yes, you can use Bar Keepers Friend on fireclay sink. Bar Keepers Friend is a cleaning product that can be used on a variety of surfaces, including fireclay sinks. When using Bar Keepers Friend on a fireclay sink, it is important to follow the instructions on the product label. Bar Keepers Friend can be used to clean both the interior and exterior of a fireclay sink. To clean the interior of a fireclay sink, first wet the surface with water. Then, sprinkle Bar Keepers Friend onto the wet surface and scrub with a non-abrasive sponge or cloth. Rinse the sink with water and dry with a soft cloth. To clean the exterior of a fireclay sink, first wet the surface with water. Then, sprinkle Bar Keepers Friend onto the wet surface and scrub with a non-abrasive sponge or cloth. Rinse the sink with water and dry with a soft cloth.