Hello ZGGTC is "Guangdong Jewelry, Jade and Precious Metals Testing Center", established in 1995, also known as Guangdong Quality Supervision Jewelry, Jade and Precious Metals Products Inspection Station. Why ZGGTC for short? Give you a full English name and you will understand, "China Guangdong Gem&; Precious Metal Testing Center ",currently there are several jewelry quality inspection points in Guangdong, which are located in Guangzhou, Dongguan, Foshan, Sihui, Shenzhen and Jieyang. You can directly search Baidu for "China GTC", which contains a brief introduction of their center.