Wool repels most liquids, but the tacky nature of nail polish means it smears when wiped rather than wicking away. Blotting wet nail polish will force the liquid into the wool fibers. If you cannot immediately treat the stain with nail polish remover, the best course of action is to allow it to dry undisturbed. Unfortunately, a highly pigmented nail polish, like red, poses additional problems if the stain is allowed to set. Even after you have removed the crust of nail polish, you may still need to remove the color transfer stain left behind.
Removing the Nail Polish and Stain
Read the label on the clothing. If it says "dry clean only," do not attempt to remove the nail polish yourself. Instead, take the garment to your dry cleaner.
Test a small area of the sweater with nail polish remover for colorfastness. If the dye from the wool does not bleed, proceed with the removal. Acetone or acetone-free nail polish remover are appropriate. Acetone will work faster and remove more of the nail polish color but has a higher likelihood of affecting the wool dye.
Turn the sweater inside out and arrange the nail polish stain over a bowl.
Pour a small amount of nail polish remover over the area of the stain and allow it to set for 5 minutes. Reapply the nail polish remover as necessary to keep the stain saturated and rinse away the nail polish.
Turn the sweater right side out to expose any remaining nail polish and blot it lightly with a cotton ball soaked in nail polish remover. Do not scrub at any remaining nail polish or you will grind it into the wool.
Lay the fabric over the bowl again and flush with water.
Examine the area of the nail polish stain. If there is still a red discoloration but no nail polish crusted to the fabric, repeat steps 4 through 7 with hydrogen peroxide to remove the discoloration.
Wash the sweater according to your usual procedure.
How to Test for Colorfastness
Turn the sweater inside out to expose the seams.
Soak a cotton ball with the nail polish remover of your choice.
Blot one of the seams with the cotton ball to saturate the wool. Check the cotton ball for any dye transfer.
Allow the nail polish remover to set for 5 minutes. Blot on more nail polish remover as necessary to keep the area saturated. Continue checking for dye transfer.
Rinse the area with cold water and note any fading or dye in the rinse water. If there is no color bleed, proceed with the removal of the nail polish stain.