To wash or not to wash. That is always the question when you have an old/vintage/heirloom quilt that is dirty. Most experts would simply tell you no - don't wash it. But some will also tell you to go ahead, clean it, but very gently. So, what's the real answer?
Well, the real answer is -- it depends! How dirty is it? Try carefully vacuuming it by putting a layer of tulle over the nozzle on your vacuum's upholstery attachment. Put a clean sheet on the floor or on a bed. Please the quilt you want to clean on top of the sheet. Slowly and gently go over the quilt with the covered nozzle barely touching the quilt. If possible, use a low suction setting (my vac doesn't have this option). Turn the quilt over and vacuum the back side. Did this help "clean" the quilt? If not, there are other options.
You can gently wash your quilt in the bathtub. This is definitely risky, and should only be attempted if the quilt is truly dirty and/or stained. But first make sure the quilt can take the cleaning. If the fabric is torn or worn, or not even there in places, don't wash it. Washing it will probably cause more damage to the fabric. If the fabric is intact, next consider the age and the colors. The age will often tell you if the colors are fast or if they will bleed. If you can, test the most inconspicuous spot you can find where a color abuts a light fabric. Lightly mist a small area with cool water. Let it sit. Did the darker color bleed onto the light color? STOP. No matter how dirty the quilt is, it is better than ending up with a tie-dyed quilt of bleeding colors. If the colors didn't bleed, there is a good chance they are fast and can be washed.
Wet cleaning a quilt taking time. Start your project early on a warm, dry day. It will take most of the morning to wash the quilt, and about 24-hours to dry it. First clean the bathtub and rinse away all residue from the cleaning agent. Line the tub with a clean white sheet. Fill the tub half full with cool/tepid water. If the quilt is really dirty you may want to add a quilt soap such as Orvus (available at most quilt shops). Some people suggest using Oxyclean as a soak but we really don't know the long-term effects of this agent so I don't recommend using it. Orvus has been proven safe for vintage fabrics but you can clean your quilt without detergents of any kind. Just soak it in plain water.
Another alternative for washing your quilt is to soak it outside on a sunny day. Follow the steps above but use a child's swimming pool lined with a sheet instead of a bathtub (unless you have an outdoor tub!) Set it in a shaded area or cover the quilt with another clean sheet.
Either way, put the quilt in the tub, on top of the sheet, in sort of an accordian fold. Make sure the water entirely covers the quilt. Then soak, soak, soak. Check the water every now and then. If it's dirty, drain and refill. Do not let the water run directly onto the quilt. Fold the quilt and sheet(s) back out of the way while filling the tub/pool. Continue soaking/draining/filling until the water is clear. At this point, the quilt is probably as clean as it is going to be.
Drain the tub or pool. Let the quilt and sheets sit until as much water as possible has drained. Now, get a partner to help with the next step. DO NOT LIFT THE QUILT ALONE! Did I state that loud enough? DO NOT WRING THE QUILT! Got that one too? With your partner at one end of the tub and you at the other, gather up the quilt in the sheet -- lifting by the sheet, not by the quilt. It's going to drip and be messy, but please resist squeezing the quilt. Let it drip, then place it in a tub or bin to carry outside. Once outside, choose a shady or part shade spot. You can dry the quilt on the lawn, but it will dry faster if you can provide airflow both on top and on the bottom. You can do this by placing a couple of clean screen doors on some sawhorses and placing the sheet/quilt layers on top of the screen doors. If you don't have a way of keeping it off the ground, unfold the wet sheet and spread it on the lawn. Very carefully unfold the wet quilt and spread it out on top of the sheet. Do not pull the sides, just gently open the quilt on top of the sheet. Now taken a second clean sheet and spread it on top of the wet quilt. This sheet protects the quilt from the elements, such as birds and other animals, tree sap, the neighbor's dog, etc. Now wait. And wait. And wait. It is going to take a while for the sheet to dry -- the warmer and drier the weather, the faster the quilt will dry, but it still isn't going to be in any hurry and neither should you. Eventually it will be dry and you will be able to pick up the quilt and enjoy its new clean beauty.
Here are a couple web sites with more information on cleaning quilts: http://www.museum.msu.edu/glqc/quiltcare.html and