You may have smelled it before you saw it, but there's no denying the dismay associated with finding mildew on silk garments. Mildew is a form of mold that festers in damp, warm locations where there is little to no air movement or sunlight. Mildew often discolors silk, which actually can work to your advantage since wet-cleaning the item -- versus dry-cleaning -- represents your best chance of removing the stain with hydrogen peroxide, which is nontoxic and mild.
Put on a pair of protective gloves. Take the silk item outdoors and remove as much of the mildew as you can with a soft brush. Throw away the mildew by wrapping it first in a paper towel and then in a plastic bag.
Dry out the silk item in the sun. Spread it out in a sunny location indoors and wait until it is warm to the touch.
Test the colorfastness of your silk garment before giving it the full hydrogen peroxide treatment. Clip a piece of hidden fabric, such as from a hem or shoulder seam. Soak the fabric swatch in full-strength hydrogen peroxide -- meaning no water -- for one hour. Rinse the swatch, dry it and compare it to the color of the garment before deciding whether to proceed.
Add about 10 ounces of hydrogen peroxide for every gallon of warm water you fill in your washing machine. The water should be no more than 100 degrees Fahrenheit. If you're running a full load, add 64 ounces of hydrogen peroxide -- that's four 16-ounce bottles, the size most commonly found at stores. Let the machine agitate the water and hydrogen peroxide, then turn the washing machine off. Put the silk garments in the washing machine and let them soak for up to three hours.
Choose the most gentle agitation cycle on your washing machine. Complete the washing cycle. Then allow the garments to drip-dry on hangers in a warm location.