Methods of altering the color of a diamond by irradiation and high-pressure/high-temperature processing

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.

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.