Look on the inside of the ring band for a symbol that indicates the type of metal it's made of. Diamonds are almost always set in gold but can also be set in platinum. The most common types of gold are yellow and white, and the symbols 14K, 18K, 22K and 24K indicate the purity. The higher the number, the more valuable the ring. Platinum is even more valuable than gold and can be identified with the symbols 900Pt, Pt900 or 900Plat.
Check for dents and chips in the metal and identify if the ring has a modern setting or is an antique.
The Four Cs
Use "The Four Cs" to check the diamond quality: cut, clarity, color and carat weight.
The cut includes shapes like round, princess, marquis or oval. Unique shapes or cuts add to the value of the ring.
Hold the ring under good lighting to check for the color and clarity of the diamond. Look to see if there's a visible color to the diamond; it might have a yellow or blue tint to it. Also see if you can spot any flecks or dark smudges. These imperfections occur naturally, but do decrease the value.
Check the carat size of the diamond. The size greatly affects the value and can range from a small half-carat to much larger (Beyonce's engagement ring is 18 carats!).
Make an appointment with a local jeweler for an appraisal. Feel free to ask questions about the value they give the ring so you understand its worth.