Today a couple of the nation’s largest jewelry retailers are arguing in a federal courtroom in Ohio. At issue is a multi-million dollar ad campaign by the diamond retailer Zales. The ad claims that Zales’ Celebration Fire diamond is the most brilliant diamond in the world. Sterling Jewelers, the company that owns Zales’ competitors Kay and Jared, says Zales’ has to take back its superlative.

Zales’ claims the lawsuit is without merit. “Our advertising was based upon testing by qualified independent laboratory and our ads make that clear” said Roxanne Barry, the director of investor relations for the Zale Corporation.

Fred Cuellar, author of the number-one selling book on diamonds, “How to Buy a Diamond,” says it’s very easy to tell if Zales’ claim is true.

“It’s simple, there’s a formula you follow,” Cuellar says. “Efficiency rating times amplified light return equals weighted light return. Remember, a photon of light is a boson. Bosons are not Fermions. Am I losing you?”

Cueller broke it down in simpler terms. He said if Sterling, the company that is suing Zales, argues that the brilliance of a diamond is subjective, “They’re wrong and they’re toast.”

But Cueller says if Sterling argues that Zales didn’t do the proper test to determine the brilliance of the diamond, then they have a case. “I studied everything they did with the Celebration diamond and they didn’t follow the protocol and so they actually can’t make the claim based on the way they did the tests on their 50-something stones.”

If Zales loses the case, it will have to pull its ad campaign in the midst of the holiday season.