You can't go wrong if you hand wash. If that's just too much work, use the hand or delicate wash setting on your washing machine in a lingerie bag. Use a mild detergent such as Woolite, The Laundress or other brand designed for delicates. Check color fastness by treating a hidden part of the clothing if necessary. Hang or towel dry.
Rayon, silk and 100% cotton should be hung. Cotton blends, polyesters, spandex blends should go in a drawer.
Here are some specifics based on fabric type.
Rayon
Made from trees, this soft, drapey fabric is weakened when wet. Use cold water and line dry. Turn inside out to iron, and use a low setting with no steam. Iron a small area at a time to prevent stretching.
Silk
Soak the fabric in lukewarm water with a mild soap for about 5 minutes or less. . Rub stains very lightly under the soap-water. Rubbing too hard can damage the silk pajamas irreparably. Rinse with water containing 1/4 cup vinegar to remove the soap and help restore shine. Your final rinse should be cold water alone. Spread your silk pajamas or nightgown out on a towel and rolling it up to wring out the excess water. Leave the silk pajamas on the towel and let it dry somewhat. Iron inside out on low while still damp.
Soft Polyester, Spandex
Hand or machine wash in a lingerie bag on the setting. Depending on the dampness, towel or line dry. You don't want it to stretch, so if it's very damp, start by wringing your nightgown or pajamas in a towel. Dryer heat destroys wicking properties, and deteriorates elastic.
Cotton/Batiste
Although cotton is durable fabric, we recommend always using a lingerie bag. And even though hot water is the general rule for cotton, we say use cold water for cotton or cotton blend Margaret Lawton nightgowns and pajamas. It's ok to tumble dry a few minutes on low, but take your beautifyl garment out of the dryer while it's still damp and line dry to finisTurn inside out to iron. For cotton, usually you'd use steam and a high setting, but for your Margaret Lawton nightgown we'd suggest iron the garment damp at a low or medium setting.
Nylon
This durable fabric may be washed in the washing maching, with warm water and put in the dryer on low. If needed, iron on low.