We can confirm through the logo on the certificate that the testing organization that issued the certificate is approved by those special qualification certifications. Generally, the logo that appears on the certificate is "CMA".
"CMA" is the English abbreviation of China Metrology Accreditation. It is a comprehensive certification and evaluation of the testing ability and reliability of testing institutions by the metrological administrative department of the people's government at or above the provincial level according to the provisions of the People's Republic of China and the National Metrology Law. This sign only means that the institution is a unit that has passed the measurement certification review, and it is a necessary qualification for any unit that issues a jewelry appraisal certificate. The inspection report marked with "CMA" can be used for product quality evaluation, results and judicial appraisal, and has legal effect.
Step 2: Description of appearance (check the model)
The next step is to confirm whether the purchased jewelry and jade are consistent with the samples described in the certificate, including the photos of the samples, the weight on the label and the weight on the certificate, and whether the appearance and description of the ornaments correspond to each other.
photos are the direct evidence to distinguish different jewels and jade, and the identification certificate photos are clear and accurate, which will greatly increase the difficulty of forgery. However, in some cases, it is difficult to distinguish because the jewelry styles are similar and the photo features are similar. In this case, the accurate weight is another valid data that can be verified. In addition to photos and weight, the appraisal certificate will also provide some distinctive appearance features, such as the sugar color of jade, the size of bracelets and so on.
Step 3: Test the content (the most important content)
This step should be the test content that we are most concerned about, and we should know which content on the certificate is the most important.
diamond grading certificate: the most important thing to pay attention to is the color grade and clarity grade of the diamond, and some certificates also have the cut ratio of the diamond.
certificate of purity inspection of precious metal ornaments: the most important thing is, of course, the type and content of precious metals.
jewelry and jade appraisal certificate: the inspection conclusion is the most important. According to the national standards, natural jewelry and jade are no longer marked with the word "natural", but the artificially treated or artificially synthesized gems must be clearly stated, such as: the conclusion is "ruby", indicating that this ruby is purely natural; "Ruby (treatment)" indicates the specific treatment method, indicating that this ruby is a natural gem, but it has been artificially treated in some way to improve its appearance; "Synthetic ruby" means that ruby is not naturally produced, but a purely artificial laboratory synthesis.
"Remarks" column: Generally, some relatively special samples are encountered in the testing process, which will be explained and noted in the remarks. For example, in the appraisal certificate of Hetian jade, once the surface treatment is involved, the specific treatment method will be indicated in the remarks.
step 4: official seal or inspection mark
in order to prevent the certificate of appraisal institution from being counterfeited, the appraisal certificate must be stamped with the official seal of the company, and the red official seal as the inspection mark is often not printed integrally with the certificate, but stamped after inspection.
nowadays, some large authentication machines are carrying out heavy anti-counterfeiting. For example, in the new certificate issued in 27, Xinjiang Rock and Mineral Gem Quality Inspection Station also added the function of online inquiry. When inquiring, you need to enter the batch verification code and enterprise verification code, so that consumers can verify it in a convenient way and find out the relevant information of the jewelry and jade purchased online.
Step 5: Understand the standards
The general appraisal certificate will also indicate the basis standards for the identification and discrimination of jewelry and jade. The current national standards specifically include:
GB/T 16552 jewelry and jade names; GB/T 16553 jewelry and jade identification; GB/T 16554 diamond classification; GB/T 1843 Nondestructive testing method for precious metal jewelry content: X-ray fluorescence spectrometry; GB 11887 Rules and naming methods for purity of precious metals in jewelry.
If you see that the certificate has one or two of these standards, you can know what standards the jewelry and jade are tested according to. In addition, the certificate should also have the signatures of more than two appraisers and the appraisal date of the certificate. After understanding these five parts, whether your favorite baby is true or not and whether the certificate is consistent will come to the bottom.
Step 6: Understand the basic knowledge
The following are the definitions of terms commonly seen in jewelry appraisal certificates:
Color
Color is the feeling produced in the brain by the optic nerve of the fundus in response to light waves (visible light from 39nm to 78nm). After visible light is selectively absorbed by an object, the color produced by the mixing of its remaining light waves is the color of the object.
optical character
refers to various phenomena caused by materials acting on the direction and propagation direction of incident light, including homogeneity, heterogeneity, non-isotropic body axis, positive and negative optical properties of materials.
optical isotropic body isotropic material
refers to a substance with the same optical properties in all aspects, which is called isotropic body for short. The equiaxed and amorphous materials are optical isotropic body.
optical non-isotropic body anisotropic material
refers to substances with different optical properties in all directions, which is called non-isotropic body for short. Except for equiaxed and amorphous materials, they are all optical non-isotropic body.
refers to a crystal that has two special directions (two optical axes) and does not undergo birefringence when light is incident parallel to these two directions. The crystals of orthorhombic system, monoclinic system and triclinic system are biaxial crystals.
refractive index birefringence
The ratio of the propagation speed of light in air (or vacuum) to that in gem materials is the refractive index, also called refractive index.
the maximum difference between two or three principal refractive indexes in non-isotropic body is birefringence, which is also called refractive index (or refractive index).
absorption spectrum
refers to the spectrum produced by selective absorption of continuous spectrum light when it irradiates jewelry and jade materials. In a narrow sense, it refers to the phenomenon that the spectrum produced by selective absorption in the visible light (7-4nm) appears as black bands or black lines on the spectrum.
lustrous luster
the ability and characteristics of material surface to reflect light. According to the strength of luster, it can be divided into submetallic luster, semi-metallic luster, adamantine luster and vitreous luster. The special luster caused by aggregate or surface features includes: greasy luster, waxy luster, pearly luster, silky luster, etc.
transparency
refers to the degree of light transmission of jewelry and jade materials. It can be divided into: transparent, semi-transparent, translucent, semitransparent and opaque.
ultraviolet fluorescence
refers to the visible light waves generated when the jewelry and jade are irradiated with ultraviolet light. According to the intensity of light, it is divided into: strong, medium, weak and none.
fire dispersion value, dispersion value
when white light shines on transparent faceted gemstones, the phenomenon that the gemstones show spectral color flicker due to dispersion is called fire color.
dispersion value is the physical quantity of dispersion intensity (i.e. fire color intensity) of reflective materials. Theoretically, it is expressed by the difference between the refractive index of the material relative to red light (B=686.7nm) and that of violet light (G=43.8nm). The greater the difference, the greater the dispersion intensity (the stronger the fire color).
density
the density of a gem refers to the mass of a substance per unit volume. The unit is g/cm3.
hardness
hardness refers to the ability of gem materials to resist external mechanical effects such as scoring, pressing or grinding. The hardness of gemstones is expressed by Mohs hardness in mineralogy.
cleavage fracture cleavage, fracture, parting
cleavage refers to the property that a crystal splits in a certain crystallization direction and becomes a smooth plane under the action of external force. Cleavage is divided into extremely complete, complete, medium and incomplete.
fracture refers to the nature of irregular fracture surface of crystal under the action of external force. Common fracture types are: uneven, serrated, shell-like and so on.
cleavage is the property that a crystal breaks along a certain crystallization direction under the action of external force (for example, the interface between two crystals).
internal character
refers to solid, liquid and gas inclusions, special types of inclusions (such as negative crystals) and phenomena related to the crystal structure of gemstones. Such as: growth line, ribbon, twine, cleavage, cleavage, etc.
external characteristics
external characteristics are divided into the external characteristics of crystals and the external characteristics of cut gemstones.
The external characteristics of crystals refer to the special phenomena related to crystal structure besides crystal shape, color, transparency and luster, such as transverse grain, longitudinal grain, twin grain, growth pits, erosion and mound dissolution.
the external characteristics of cut-grinding gemstones refer to the phenomena left in the process of cutting, grinding and polishing, such as scratches, polishing lines (marks), micro-notches, cavities, damages, burn marks, impact marks, whiskers, extra facets, sharp or smooth edges, etc.
optimization treatment enhancement
all methods used to improve the appearance (color, cleanliness or special optical effect), durability or usability of jewelry and jade except cutting and polishing. It is divided into two categories: optimization and processing.
optimizing reinforcement
The traditional and widely accepted optimization treatment method shows the potential beauty of jewelry and jade.
treating
an unconventional and not yet accepted optimization method.
Common optimization methods
Optimization methods: heat treatment, bleaching, wax dipping, colorless oil dipping and dyeing (chalcedony, agate).
treatment methods: soaking in colored oil, filling (glass filling, plastic filling or other hard materials such as polymers), soaking in wax (turquoise), dyeing, irradiation, laser drilling, film covering, diffusion and high temperature and high pressure treatment.