I finally got organized enough to dispose of some old rings. Took the same batch to two different jewelers who have been advertising in the Blade.
Salesmen at store "BF" identified the pieces as 10 and 14-carat gold (plus some worthless stuff) and offered me $175. On the same day, store "DF" identified the hoard as 14 and 18-carat gold (plus worthless pieces) and paid me $425.
I'm glad I shopped around, but I am a little surprised that people at the first store were either unable to recognize 18k, or were giving inaccurate information. I suppose it's possible that world gold prices jumped dramatically while I was driving between stores!