RetroClean--it's a miracle stuff!

Thank you to everyone for your suggestions! You've given me the courage to spot-clean it, using a tiny dot of dishwashing soap, distilled water, and a soft brush. I will know more when it's completely dry tomorrow, but this evening I think the stain has at least faded. If I think it's not come out completely and needs more work, I'll try the RetroClean. This was a smudge of soot from the hearth, nothing more. But it did make a bit of a mess!

Anything that can't be washed and dried in washer and dryer gets donated.

I wash and dry all my quilts as soon as I finish them. I have a few hand quilted ones from years ago. They are stored away. I did wash and dry them when finished.

Synnove- I was the first one who responded but the more I think about it the more I feel you aren't going to hurt in by regular washing and drying. Most of my quilts were hand quilted by me (not the antique ones I mentioned before) and they've washed up beautifully. As long as they are secure I don't see a problem.
The others have given you good advice though. One thing I wouldn't do is take it to the dry cleaners. Nope on that!
Also I don't use fabric softener of any kind.

I have washed my hand done Grandmother's Flower Garden (made by my grandmother, not me) numerous times in the last 60 years. The fabric and stitches are fine. Pretreat with an Oxiclean gel rub on and wash it.