Expert Jewelry appraiser expert witness and certified gemologist, Charles Carmona has offered coin, gemstone and jewelry appraisal services since 1980

Jewelry Appraisal Services

Gemstone Weight Estimation


Since 1980, Guild Laboratories, in Los Angeles, CA has been the most relied upon source for securing expert gemstone grading, gem identification and independent appraisal and valuation for diamonds, gemstones, jewelry and currency.

Guild Laboratories president Charles Carmona, GG ASA has built this reputation by delivering fair and impartial valuation reports and consultation backed by decades of research and appraisal experience.

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Gemstone Weight Estimation Handbook

This thoroughly comprehensive manual does the difficult task of estimating carat weights of mounted gemstones, calculated by their dimensions and shape, with over 300 pages of tables listed, and gemstone type.

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Guild Gem Lab in Asia

Providing efficient, expert and thorough gem testing in 3 strategic Asian locations, Guild Gem Labs in Hong Kong, Shenzhen and Bangkok offers its clients colored gem testing and origin determination services. Learn more about Guild Gem Labs at

Appraisal and gemology services

Guild Laboratories is a trusted source for all of your gemological needs.

With decades of experience, we provide the highest quality appraisal services for diamonds and gemstones, jewelry, coins, and decorative art objects.

We offer consultation services, and provide experienced expert witness and litigation support to private and governmental agencies. See our SERVICES page to review our complete schedule offered at Guild Laboratories.

Client List
  • Guild Gem LabShenzhen
  • Guild Gem LabBangkok
  • Guild Gem LabHong Kong
Guild Gem Lab1 Guild Gem Lab2 Guild Gem Lab3

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