Pour 2 tablespoons of ammonia into a bucket. Add 1 quart of warm water.
Dampen a clean cloth with the diluted ammonia solution. Wring out excess moisture.
Wipe stained areas of the quartz countertop with the ammonia solution until the stain material is softened. Scrape the softened stain matter with the edge of a credit card to remove it from the surface.
Remove any remaining stains by rubbing them with a nonabrasive cleaning pad that's safe for quartz countertops.
Place a drop of dishwashing detergent on a clean, damp cloth. Wash the surface of your quartz countertop to clean it. Rinse the counter with a damp cloth. Dry it with another cloth.