Opal Identification and Value
Table of Contents
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Foreword
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vii
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Preface
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ix
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1. Getting Started
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1
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Buying Opal
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1
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Valuing Opal
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2
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Opal Myths
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3
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2. About Opal
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5
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What Is Gem Opal?
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5
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Types of Opals
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6
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The Source
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6
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Cutting Opal
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7
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What Makes a Good Opal?
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8
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3. Identifying Type
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11
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Types of Opal
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11
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Determining the Type of an Opal
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14
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Identifying Set Stones
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20
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Importance of Type
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21
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Summary
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22
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4. Natural, Synthetic, Simulant, Dyed
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25
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Synthetic
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25
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Simulants or Imitations
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26
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Dyed Opal
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28
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Conclusion
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30
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Summary
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30
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5. Base Color
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31
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What is Base Color?
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31
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Definitions of Base Color
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33
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Determining Base Color
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35
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Black Opal Criteria
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36
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Crystal and Semi-Crystal Criteria
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40
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Base Color and Value
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42
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Summary
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43
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6. Brightness of Fire
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45
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Brightness Standard
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45
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Light and Brightness
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47
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Developing Brightness Criteria Stones
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48
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Judging Brightness
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50
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Brightness is Most Important
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51
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Summary
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52
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7. Fire Color
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53
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Dominant Color
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53
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The Multicolor Rule
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56
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Hue, Saturation and Intensity
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57
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Judging Fire Color
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58
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Summary
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58
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8. Fire Pattern
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59
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Patterns Defined
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59
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Harlequin Pattern
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61
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Rare Patterns
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62
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Picture Stones
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66
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Determining Pattern
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67
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Summary
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68
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9. Consistency and Directionality
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69
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Consistency
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69
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Directionality
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70
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Summary
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71
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10. Cut, Inclusions and Weight
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73
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Cut
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73
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Weight and Thickness
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75
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Weight and Thickness in Calibrated Oval Opals
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77
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Inclusions
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79
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Cracks and Crazing
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79
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Stability
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81
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Weight
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83
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Cut, Inclusions, Cracks and Value
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84
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Summary
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84
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Weight Estimation Formula Supplement
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86
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Weight Estimation
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86
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Standard Shaped Cabochons
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86
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Example
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87
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Bulge Factor
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88
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Freeform Stones
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89
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11. Properly Set Opals
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91
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Protecting the Opal
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91
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Custom Designers
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93
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Sizing Rings
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95
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Inlayed Opal
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96
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Summary
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97
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12. Solid Opal Prices
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99
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Opal Prices
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99
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Estimating Price
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102
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Example
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106
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Summary
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109
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Characteristics Adjustment Supplement
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110
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Price Adjustments
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110
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13. Boulder Opal Prices
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117
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Types of Boulder Opal
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118
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Characterizing Boulder Opal
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120
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Pricing Boulder Opal
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124
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Example
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126
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Pricing Boulder Matrix
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128
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Andamooka Boulder
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129
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Conclusions
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129
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Summary
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129
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Boulder Adjustment Supplement
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130
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14. Other Opal Prices
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133
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Pricing Doublets
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133
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Triplet Prices
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136
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Summary
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141
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15. American and Canadian Opal
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143
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American Opal
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143
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Nevada Opal
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143
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Idaho Opal
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145
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Oregon Contra Luz
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146
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Arizona Blue Opal
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148
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Louisiana Opal
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148
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British Columbian Opal
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148
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Summary
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150
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16. Other Locations
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151
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Mexican Opal
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151
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Brazilian Opal
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154
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Honduras Opal
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155
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Indonesian Opal
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156
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Ethiopian Opal
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156
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Summary
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157
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17. Opal Jewelry
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159
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Commercial Settings
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159
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Manufactured Jewelry
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160
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Designer Jewelry
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160
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Designer One-of-a-Kind
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161
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Antique / Estate Jewelry
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162
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Opal Design Treatments
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172
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Summary
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178
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18. Collections and Carvings
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179
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Collector Pieces
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179
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Fossils
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182
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Carvings
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183
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Summary
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185
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19. Buying Opal
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187
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Finding Opal
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187
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Buying Opal
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189
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Buying in Australia
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191
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Summary
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192
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20. Conclusions
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193
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Glossary of Terms
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195
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Index
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200
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Acknowledgements
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205
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Photographers
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206
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Designer Contacts
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207
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Other Books By Paul B. Downing
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208
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About the Author
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212
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