It is common sense to buy diamonds and see certificates, and GIA certificates are the most recognized by domestic consumers. Gia diamond certificate is not only an important way to know the grade of diamonds, but also plays an important role in buying diamonds. Gdtc is a certificate issued by Guangdong Jewelry Appraisal Center. The provincial appraisal center is reliable, but its authority is almost not as good as that of the national level, such as NGTC.