So you don't live in Japan? What can you do? Below are a few cleaning tips, but please be forewarned - if your heart can't bear ruining a piece, be content with your treasure and don't gamble on your attempt to clean it.
Let's start with the easiest: Often a brisk rub-down with a clothes-brush will take care of the problem and give your kimono or haori a fresh look. If there is a spot sitting on the surface, say a little caked oatmeal as a souvenir left from feeding Junior, make sure it is completely dry. If you look closely and see that it is sitting on the surface of the fabric (the schmutz will cover and block the weave) then you are in luck. Removing surface debris is fairly easy. (Don't try this if the fabric is weak or brittle.) Grasp the fabric to either side of the soiled area and pull-snap briskly on the diagonal. Move your hands and repeat this operation on the opposite diagonal. This will normally cause any caked-on spot to pop or flake off. If there is still a little dusty residue, grab another segment of the garment (same weave, same color) and rub it vigorously over the spot. I emphasize using the same color and same weave. If a different weave is used, it will sometimes “polish” the spot causing it to be clean but shiny. Using the same weave will prevent this from happening. If you use fabric from the same garment, but of a different color, you run the risk of having the new color transfer (crock) to the soiled area.
If you find you have oil-based spots, they won't rub out. You will need something to dissolve the spot before it can be removed. Often, in Japan, benzene (lighter fluid) will be used. Dry cleaning fluid also works well. Be careful while doing this - both fluids are highly volatile, toxic to breathe, and toxic when absorbed through your skin.
Prepare a small piece of cloth, preferably the same color as the area to be cleaned, by placing a cotton ball in the center and bringing up the edges to form a “tissue ghost” or teruteru-bozu shape. Add a little cleaning fluid. The ball should be damp, not wet, with fluid. Gently, lightly, begin by rubbing the ball against the center of the spot, working in a circular motion toward the outer edges and beyond. Return to the center of the spot and repeat this action untilt all of the fluid has been used up and it is starting to dry on the fabric. Keep working outward until it seems as if the ball is dry, return to the center and repeat several times if necessary, until only the faintest haze of moisture may be detected on the outer edges of the circle. Rubbing and working in this circular manner will keep the cleaner from forming its own liquid stain-line. If it is a small enough spot, it may help to stretch that area in an embroidery hoop to make it easier to rub.
If you prefer to use water on a spot, approach it as outlined above.
If you have spots caused by water on your silk (sometimes a spot of water will change the way fiber reflects light, causing it to appear to be a stain), try lightly spraying the area with more water. Be frugal. Only moisten the area, and be sure to allow the sprayer to do its job in “feathering” out the spray along the outer edges of the affected area. If you go at it with too heavy a hand, you'll simply create a larger spot.
The greatest risk in laundering is presented by the dyes, not the fabric itself. I've often heard, “Oh! You can't wash silk!” Nonsense. Silk is very durable and easy to wash. It is the dyes you have to watch out for.
There is no way that a layperson can know which dyes were used, and how well they have been set. The first red flag you should monitor is bleeding. This is especially common among synthetic dyes. Bleeding is when excess dye, or ill-set dye, comes out into the wash-water. If you are not careful, this can stain other areas of the garment. Have you ever accidentally thrown a red shop rag in with the white laundry? The red bled onto the whites making everything pink.
If you are bound and determined to wash your piece without un-stitching it, this is called maru-arai, then be prepared to use lots of water. Choose a vessel that can hold enough water to allow your garment to fit without crowding. A bathtub works well. A bathtub with a drain in the bathroom floor works even better, as does an outdoor horse-trough or kiddy pool. Fill the container to the top with cool-to-warm water while adding a little cleaning solution. Orvis® or Mane 'N Tail® (horse/sheep shampoo) work quite well. Gently lower your kimono into the water trying not to trap bubbles. As you do so, keep vigilant to spot any bleeding as soon as it starts to occur. Red linings are especially notorious for bleeding. If bleeding is noticed, continue adding water until the dye bleeding into the wash-water is carried away from the fabric. This is why it is good to have large vessel and a drain in the floor (or work outside) - you can allow the water to overflow the top. Keep flushing the container with fresh water until the bleeding stops or the well goes dry.
With gently care lift the clean kimono out of the water and gently arrange it in the drum of a washing machine, spin out the water. Replace the water in the washbasin and rinse the kimono. Do this several times if necessary - until the water runs completely clean.
Never wring the fabric. Many natural pigments used in Japanese dyeing that otherwise are quite stable, will crock if great pressure is applied to them while wet. Crocking is when a dye transfers due to contact (as when the blue rubs off an indigo dyed piece).
After the final spin, the kimono may be hung to air dry. If you have a long pole that you can run from cuff to cuff to hang the garment, you will avoid the stretch marks at the shoulder that arise from drying wet clothes on a hanger.
Some older types of gold leafing used a water-based binder (nikawa). This may dissolve away, and the gold go with it, when doing maru-arai. I don't recommend washing older uchishiki, or other gold leafed textiles, for this reason.
Do not throw your kimono in the dryer unless it is machine sewn. The stress of the tumbling action will weaken the stitching in all hand-sewn garments. In addition, if you are working with a lined piece, you may cause the various fabrics employed to shrink unevenly. Since traditionally constructed kimono are not intended to be washed as a whole garment, the fabrics are not “pre-shrunk”. Each weave has its own rate of contracting when wet. Chirimen (crepes) can shrink up a great deal, over-all kanoko-shibori may sag. Flat weaves tend to stay the same.
Without sufficient care you may wind up with a very disconfrumpulated garment - fabric sagging, fabric shrunk, and seams puckered. To help avoid this, with your still damp garment hanging from a pole with arms spread, gently tug at the weft by grasping the seams to either side and pulling until the outer fabric and the lining have flattened and stretched to an even width. Repeat this action for every panel of your kimono. Next address the collar by pulling gently along its length - taking care not to stretch out the top of the okumi panel. Lastly, gently pull, and stretch if necessary, along each of the vertical seams to straighten them out completely. All this activity will help your garment to dry more quickly and evenly, avoid some shrinkage, and make it much easier to iron.
Once your garment is entirely dry, remove it from the drying rod and gently iron it with a low steam setting. DO NOT iron any folded seams or edges completely flat. This will ruin the grace of your kimono. Instead try an old tailor's trick for ironing men's neckties - lay a thin yardstick, or piece of cardboard, butt up against the fold and then steam iron. The thickness of the ruler or cardboard will prevent the iron from creasing the fold, while at the same time giving you a clean line.
Time to get gussied up!