Wedding dresses are very commonly stored, both for sentimental reasons and for possible use by another generation or two of brides. However, rust can appear from metal hardware, such as buttons, fasteners and even hardware inside a storage chest. Although it may look as though the dress is ruined, there are proven methods that you can use to restore the piece.
Lay the gown out flat on a clean surface. Shake salt over the rust spots until covered. If you have multiple rust spots -- from multiple buttons, for example -- it's best to deal with one at a time.
Squeeze concentrated lemon juice over the salt, until it begins to dissolve into a thin paste. Let this sit on the stain for roughly 30 minutes.
Rinse the area with hot water. Repeat the process until the stain is removed or faded to an acceptable level.
Try rubbing hydrogen peroxide on the stain with a cotton ball if the salt and lemon treatment wasn't effective enough. Let this sit on the rust spots for about 15 minutes prior to rinsing.
Make a paste out of cream of tartar and distilled white vinegar if the previous two methods aren't making much of a dent. Note that this is only a good idea on pure white dresses. Rub the paste into the stains, allowing it to sit for 15 to 30 minutes prior to rinsing.