Methods of altering the color of a diamond by irradiation and high-pressure/high-temperature processing
View Patent ↗Embodiments of methods of altering the color of diamonds are disclosed. In an embodiment, a method for altering the color of diamonds includes identifying and selecting a diamond having a suitable nitrogen content, HPHT processing the selected diamond under diamond-stable conditions to alter the color of the selected diamond from a first color to a second color, irradiating the HPHT-processed diamond with an electron source having an energy between about 1 MeV and about 20 MeV so as to alter the color of the selected diamond from the second color to a third color, and annealing the irradiated diamond either under partial vacuum conditions, or under HPHT diamond-stable conditions so as to alter the color from the third color to a fourth color (e.g., pink, red, or purple, depending on the nitrogen content of the selected diamond).
1. A method of altering a color of a natural diamond, the method comprising:
subjecting the natural diamond to a high-pressure/high-temperature (“HPHT”) process under diamond-stable conditions effective to alter the natural diamond from a first color to a second color that is different than the first color;
irradiating the natural diamond with electrons having an energy effective to alter the natural diamond from the second color to a third color that is different than the first color and the second color; and
annealing the natural diamond at a temperature of 950° C. or less effective to alter the natural diamond from the third color to a fourth color that is different than the first, second, and third colors and that is pink or purple.
2. The method of claim 1 , further comprising, prior to subjecting the natural diamond to the HPHT process, identifying a nitrogen content of the natural diamond.
3. The method of claim 2 wherein the nitrogen content is no more than about 200 ppm.
4. The method of claim 2 wherein the nitrogen content is no more than about 50 ppm.
5. The method of claim 2 wherein the nitrogen content is no more than about 25 ppm.
6. The method of claim 2 wherein identifying a nitrogen content of the natural diamond includes identifying the nitrogen content via infrared spectroscopy.
7. The method of claim 1 wherein subjecting the natural diamond to an HPHT process under diamond-stable conditions effective to alter the natural diamond from the first color to a second color that is different than the first color includes subjecting the natural diamond to a temperature of at least about 1000° C. and a pressure of at least about 4 GPa.
8. The method of claim 7 wherein the temperature is between about 1800° C. and about 2500° C., and wherein the pressure is between about 5 GPa and about 10 GPa.
9. The method of claim 1 wherein the pressure is between about 5 GPa and about 8 GPa.
10. The method of claim 1 wherein the energy of the electrons is between about 1 MeV and about 20 MeV.
11. The method of claim 10 wherein the energy of the electrons is between about 2 MeV and about 5 MeV.
12. The method of claim 1 wherein annealing the natural diamond at a temperature of less than 950° C. effective to alter the natural diamond from the third color to a fourth color that is different than the first, second, and third colors includes annealing the natural diamond under partial vacuum and with the temperature at about 900° C.
13. The method of claim 1 wherein annealing the natural diamond at a temperature of less than 950° C. effective to alter the natural diamond from the third color to a fourth color that is different than the first, second, and third colors includes annealing the natural diamond at about 100 kPa and with the temperature between about 850° C. and about 950° C.
14. The method of claim 1 , further comprising pre-irradiating the natural diamond prior to subjecting the natural diamond to the HPHT process.
15. The method of claim 1 wherein the first color is brown, the second color is yellow, and the third color is blue-green.
16. The method of claim 1 wherein the natural diamond is type IaB.
17. A method of altering a color of a natural diamond, the method comprising:
subjecting the natural diamond to a high-pressure/high-temperature process under diamond-stable conditions effective to alter the natural diamond from a first color that is brown to a second color that is yellow;
irradiating the natural diamond with electrons having an energy effective to alter the natural diamond from the second color to a third, blue-green color that is different than the first color and the second color; and
annealing the natural diamond under diamond-stable conditions including a pressure of at least 4 GPa and a temperature of at least about 1000° C. effective to alter the color of the natural diamond from the third, blue-green color to a fourth color that is pink or purple.
18. A method of altering a color of a type IaB natural diamond, the method comprising:
subjecting the type IaB natural diamond to a high-pressure/high-temperature process under diamond-stable conditions effective to alter the type IaB natural diamond from a first color to a second color that is yellow;
irradiating the type IaB natural diamond with electrons having an energy effective to alter the type IaB diamond from the second color to a third color that is different than the first color and the second color; and
annealing the type IaB natural diamond at about 100 kPa and at a temperature between about 850° C. and about 950° C. under conditions effective to alter the type IaB natural diamond from the third color to a fourth color that is pink or purple.
19. The method of claim 18 wherein annealing the type IaB natural diamond includes annealing the natural diamond at a temperature of about 900° C.
20. The method of claim 1 further comprising pre-irradiating the natural diamond prior to subjecting the natural diamond to the HPHT process, wherein pre-irradiating the natural diamond includes pre-irradiating the natural diamond at a different energy level than an energy level used for irradiating the natural diamond with electrons.