Owing to the innate characteristics and growth environment of emeralds, clarity enhancement is a common practice in the trade. At present, various types of fillers have been applied to emeralds, including colorless oil, wax, resin, etc. Experienced dealers are familiar with these fillers. However, Guild Gem Laboratories found distinct green external materials in several emeralds. Is this a new type of filling? How will this discovery affect the current emerald market? In this paper, the type, causes and effects of this green external material will be explained in detail.