The holidays are popular times for engagements, and if you and your beloved are shopping for a diamond ring, consider your budget.

Last year, the average price of a diamond engagement ring was $3,200, according to the Diamond Information Center in New York. That figure represents a $600 increase over the average purchase price for engagement rings purchased in 2001.

Find a reputable jeweler, preferably one who belongs to a trade association, such as Jewelers of America, which sets high ethical standards and provides members with continuing education.

Or find a jeweler who is also a gemologist. Sandi Marino, who has worked at Seita Jewelers in Tarentum for the past 20 years, fits that bill.

Understand the four characteristics of a diamond -- color, cut, clarity and carat weight -- and how they affect a stone's value. (You can visit the Jewelry Information Center's Web site at www.jic.org to learn more.)

The color grading chart for diamonds starts at D and goes through Z. D is the grade for the finest, whitest diamonds, which are quite rare. The farther into the alphabet, the more yellow or brown there will be in a diamond. Many people buy diamonds in the E, F, G or H color range, Ms. Marino said, with G or H diamonds selling the most often.

A good way to determine a diamond's color is to ask a jeweler to set several loose diamonds against a white piece of paper.

Cut is the most important characteristic because it determines a stone's brilliance. More than a third of women prefer round diamonds but others like the square princess cut. Seita Jewelers and Henne Jewelers in Shadyside also sell a square brilliant diamond.

"This is a square diamond with the corners cut off. The pavilion, which is the bottom of the diamond, is faceted like a round cut diamond. It has more brilliance than the princess cut because of this reason. We show them the square brilliant and that's what they end up buying," Ms. Marino said.

Diamonds are rated for clarity on an internationally used scale. A diamond rated I F is internally flawless. These stones are exceedingly rare. The scale continues, using a combination of letters and numbers with the lowest end of the scale set at I 3.

"What we sell the most is anywhere between a V S 1 to an S I 1. There are steps in between. Every step up or down makes a difference in the price of the diamond," Ms. Marino said.

Today, young people are buying anywhere from three-quarters of a carat to a carat and a half, Ms. Marino said.

It's wise to buy a certified diamond. Diamonds are certified by the Gemological Institute of America, the International Gemological Institute or the European Gem Laboratory.

Helena Krodel, a spokeswoman for the Jewelry Information Center in New York, said that buying a certified diamond is "the best way to ensure that you are getting what you pay for in addition to shopping at that reputable jeweler."

Certification, done by an independent organization, is "somebody vouching for what your jeweler is telling you," Ms. Krodel said.

A certification shows the cut and proportions, the diamond's color, its exact carat weight and a map of the stone's clarity.

Jewelers who buy from diamond suppliers have the option of buying a certified or non-certified diamond. Certification costs about $200.

But you do not have to have a diamond certified to insure it, Ms. Marino said. All you need is a jeweler's appraisal.

If you are determined to surprise your sweetheart, Ms. Krodel said, assess her personality, lifestyle and existing jewelry before making the selection.