To paraphrase Wikipedia, silk is a natural protein fiber produced by certain insect larvae to form cocoons. The insect most commonly used in silk production is, obviously, the silkworm.
Silk fiber has been used since prehistoric times. An individual strand of silk is smooth but not slippery (unlike its synthetic counterparts) and it’s strong for its weight, although it will lose strength when wet. It’s most often spun into fine yarns and used to create luxury fabrics of various types, including satin, taffeta and charmeuse. The distinctive rough (aka “slubby”) texture of dupioni and shantung silk fabrics are from using silk fibers that contain natural bumps and lumps from the source cocoon.
Because creating silk is a labor intensive process, it remains a luxury fiber, even in this age of mass production. Silk fabric can be used in many ways: formal wear, lingerie, and even day to day wear if you can afford it.
Because it’s expensive, there are several artificial yarns out there that try to do the job of silk, such as nylon and polyester, but none of them will have the breathability and absorptive properties of real silk. I love using it, but can rarely afford to do so! Alternative options include polyester, acetate and rayon.
Silk is proverbially strong and it can last a long time. It’s survived in archeological sites when all other fibers have disintegrated. Silk fabric would be worn beneath armor by warriors from China to France as its strength proved very useful in stopping inconvenient arrows and other sharp things. On the downside, silk is susceptible to “sun rot” – the fiber can weaken when exposed to sun over an extended period of time – and many costumers take care not to wear it directly against the skin as sweat and body oils can negatively impact the fiber over time.
As with all natural fibers, silk can and will shrink – up to 8% according to Wikipedia. Even if the seller assures you that your fabric is “pre-shrunk” you should always wash your fabric how you intend to wash the finished garment, and dry it the same way, before you cut it. Even if you plan to handwash the finished garment and lay it flat to dry, do that to your un-cut fabric. It’ll help wash off any chemical residues from the textile mill and potentially save you from unpleasant surprises down the road.
When pressing silk, always use a dry iron (no steam) and a press cloth.
Silk will shrink less when sent to a dry cleaner, but of course, that’s going to increase your cost of keeping the garment and, besides, if your costume is heavily embellished, you’re going to want to clean it at home. Use a mild detergent and wash by hand, laying it flat to dry.