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