Precious Coral's Chromatic Mechanism And Appraising

Members in Coralliidae,also called precious corals,are of the most valueable marine resourses,which has been used as jewlery and sculpture materials for over1000 years both in estern and western cultures.The beauty of precious corals is mainly about the color.The intense red?pink colors of precious color are widely welcomed by people all over the world,especially people in East Asia.Species in Coralliidae are distributed worldwide,differernt species show characteristics in thier own ways.This paper measures the gemological properties of red coral such as refractive index,fracture,hardness,and density,and studies the issues that need to be noted in the process of wearing and placing red coral.In addition,it measures the color of 145polished red coral specimens in the CIELab uniform color space by using the X-Rite spectrophotometer and thus determines relationships between color parameters and change trends.By measuring the Raman spectra of different colors of red coral specimens,adopting statistical analysis to determine the functional groups in the red pigments that cause red corals,and matching the content of functional group with the color parameters,it is determined that the higher the content of the pigment,the lower the color brightness value L*of the red coral,and the smaller the hue angle h₀,the darker and redder the color of the red coral.After comparing and analyzing the color changes of red coral under the three standard light sources of D65,A,and CWF,it is determined that the D65 light source is the most suitable light source for the display and color evaluation of red corals.A cluster analysis is performed on the color of red coral under D65 light source,and red-dark red corals are classified as five categories including dark red?L*?[29.55,36.51],a*?[21.13,28.49],b*?[8.64,12.63]?,crimson?L*?[33.11,39.19],a*?[27.33,32.22],b*?[11.96,16.15]?,intense red?L*?[35.22,44.50],a*?[33.85,39.38],b*?[17.86,22.39]?,red?L*?[35.22,44.50],a*?[33.85,39.38],b*?[17.86,22.39]?,orange-red?L*?[40.60,44.01],a*?[39.22,46.44],b*?[21.34,25.07]?.The growth process of the axial bone in the red coral family is concluded by using field emission scanning electron microscopy to observe the microstructure of the red coral original branch and it is found that there are recrystallizations in the calcite in the exoskeleton of some red corals.The elemental content of the red and white areas of the red coral is measured by using an EDS.It is concluded that the white area of the red coral has lower organic content than the white area,while the white area has higher calcium content than the red area.