Remove collar stains by dabbing them with a cloth dampened with a mixture of, in 3 equal parts, washing up liquid, ammonia and water. Scrub with an old toothbrush. Rinse & dry.
Alternatively, dab the ring with a clean cloth dampened with warm water and white vinegar. (One tablespoon of vinegar to a bowl of water)
When using ammonia, open the windows, and avoid breathing the fumes that this product produces. Wear a mask if possible.
On a cotton garment rub the stain with shampoo and launder as usual
On a silk garment sprinkle talcum powder on the stain, cover with several sheets of absorbent paper and then iron over on a low setting. Repeat until completely eliminated.