Most pearls that are on the market today are formed when an irritant is introduced inside an oyster or mussel.As a defense, the oyster or mussel will secrete nacre, which coats the irritant in layers. The smaller the introduced irritant, the longer it takes to build up the layers of nacre needed to produce a large pearl. I wondered how long it took to make these 10mm black pearls and what size irritant was used. The pearl strand was cleaned with mild soap and water (at first the water turned very dark and cloudy) until the water ran clear. Note: Since I was going to take the strand apart, I did not worry about submerging the stringing medium, which will weaken it. A soft cloth or a soft wet cloth is all that should ever be used on pearls. Also, do not use hot water or ultrasonic cleaners on pearls as they can damage the outer layer. Wearing pearls frequently keeps them from drying out.