Clara Certified Blue Sapphire (Neelam) 7.5Cts Or 8.25Ratti Stunning Silver Ring Bis hallmark and govt recognised laboratorty certificate Pure silver tends to tarnish and become yellow and eventually black after sometimes. But it can be easily cleaned by gently rubbing the ring with colgate powder. Slight variation in shape of the stone is possible as no two natural gemstones are similar in shape and size. Product weight = 6.5gms Stone weight is mentioned both in carat and ratti. Ratti calculated as per 180 milligrams for 1 carat.