Hi Nancy, hope this link helps, it has all the different fabrics and materials listed on it as well as cleaning methods for each
It depends upon the kind of fabric. If you have nothing to lose I would wash them on a gentle cycle and hang them to dry
Nancy...You can drape them over a clothesline, spray on some Krud Kutter or whatever product you have and hose off. They will need to be turned and cleaned on the other side. The sun will dry, then turn for the other side. Hope this works for you if you try.
By law, there should be a fabric content tag and a fabric washing/care tag on the curtains somewhere. Check at the top/bottom seam corners or between the decor fabric and blackout fabric for the tags.
Personally, I don't feel things are really cleaned without washing in most cases. I would put them in my large front load washer (or at the laundromat) and wash on warm or cool water, gentle cycle.
IF you see any color dye runs, you can wash again (or soaking is better if you have a front load washer at home) in COLD water with table salt to set the dye. Rinse (and extra rinse if at home) in cold. There should be no more dye runs but if so, repeat the salt rinse.