Brush away as much of the mold on the cotton as possible. If the cotton material is durable enough, use a stiff bristled brush to remove the mold. If the cotton material is more delicate, brush away the mold with your hand. Do this outdoors to prevent spreading the mold around your house.
Hand-wash the cotton material promptly with soap and water.
Air-dry the cotton material outside under the sun for a few hours until it is completely dry.
Squeeze lemon juice over any mold spots that remain to dampen them. The amount of lemon juice you will need will depend on the amount of mold remaining. Sprinkle salt over the dampened areas with lemon juice. Lay the material under the sun to bleach away the remaining mold.
Rinse the cotton material thoroughly when finished.