My bowls are finished with a food safe oil finish. If used as a salad bowl, clean with soap and water and immediately wipe dry. Do not allow water to stand in the bowl. If the finish becomes dull, apply a light coat of mineral oil, wiping off the excess after ten minutes.
If the bowl is used as a purely decorative piece and not for food preparation or service, I recommend a coat of lemon oil or a similar furniture polish once or twice a year.
I have no reports of my bowls being stained by salad dressings, however rotten fruit and strawberries have been reported to cause staining.
Dishwashers will cause damage to my bowls.