White cotton clothing often becomes yellow and discoloured as a result of being washed in hard water. Hard water contains a concentration of minerals such as calcium and magnesium. The mineral build-up can make it difficult to clean the clothes properly because soil can cling more easily. Softening the water helps prevent yellow dinginess from occurring, and chlorine bleach eliminates the discolouration. A phosphate or heavy-duty detergent also helps eliminate hard water stains. Following these steps should help bring yellowed cotton back to a bright white.
Read the care tag on the clothing to determine the hottest water setting it can handle. Set the washing machine to warm or hot water.
Add 1 cup of water-softening powder or water conditioner to the water in the washing machine as the machine is filling. Add 1 cup of chlorine bleach to help remove the yellow colour. Allow the washer to fill with water. Stop the cycle once the washer fills.
Add four times the normal amount of phosphate washing powder to the washing machine. Add the white cotton clothing to the washing machine.
Allow the white clothes to soak for 12 hours or overnight.
Set the washing machine to complete the cycle without agitating the clothes so the water drains out.
Wash the white clothing in the washing machine, running it through its standard wash and rinse cycles. Do not use detergent. Instead, use 1 cup of the water softener and 1 cup of chlorine bleach.
Remove the clothing from the machine immediately. Dry the clothing by hanging it on a clothesline. Drying in the dryer may cause the yellow stains to become permanent.
Repeat this laundering process until the yellow discolouration is gone.
Add the water softener according to the package directions for best results.
Don't use more than 1/2 cup of chlorine bleach if you have a front-loading washing machine.