When sourcing antique brushes (also known as leathering brushes), you must prioritize the filament material, typically Silicon Carbide (SiC) or Diamond-impregnated synthetic fibers. For hard stones like granite, Diamond brushes are essential for durability, while Silicon Carbide is suitable for softer stones like marble. Pay close attention to the grit size range (usually from #24 to #1000); a full set is required to achieve a smooth 'leather' finish. Additionally, verify the base material, ensuring it is made of reinforced nylon or high-quality plastic to prevent cracking under high-speed rotation.