A silk comforter is a long term investment. If you take good care of it, a silk comforter should last at least 5 to 10 years, and possibly much longer. Silk is an amazing fiber in that it is remarkably strong, and yet very fragile, so much care should be taken to keep it in premium condition.
Always use a cover with your silk comforter. Although it means you won't have the silk next to your skin, it also means the oils and skin won't find their way onto or into the silk either. Using a top sheet is also advised. You can and should then launder the top sheet often (at least once a week), and the cover itself less frequently (for example, on a monthly basis). A duvet cover will preserve and protect your comforter so that frequent cleanings of the comforter itself are unnecessary. If you do use a cover, the silk comforter itself will almost never need cleaning. This is important, as the cleaning process can cause subtle damage that will accumulate if cleanings are too frequent.
If you do need to clean a silk comforter, it must be professionally cleaned. Washing a silk comforter in water yourself would almost certainly ruin it. Make sure you call around and ask the cleaners about their experience with cleaning both comforters and silk. Often cleaners that specialize in cleaning silk wedding dresses are good candidates. Although dry cleaning is a possibility, there may be trace amounts of chemical residues left behind and the process may harden the silk if done repeatedly. Professional wet cleaning is becoming more common, and is the preferred option.
"Sun curing" is the traditional way to care for a silk comforter. You should air out your silk comforter using this technique periodically, whenever it becomes heavy or starts to lose heat retention. To do so, place the comforter in the sun (with the cover on for protection) for an hour or two at the most. Because silk has the ability to absorb moisture, this process will dry it out, making it more fluffy and lighter, and improving its insulating properties. Alternatively, you may place the comforter in the dryer on extra low heat for a short time, not to exceed 30 minutes.