In a large saucepan, combine eggs and 1 teaspoon salt; cover with cold water. Bring to a boil, reduce heat, and simmer for 20 minutes. Remove from heat, drain, and cool. When cool, tap eggs with the back of a spoon to crack shells (do not remove shells). In a large saucepan, combine 3 cups water, soy sauce, black soy sauce, salt, tea leaves, star anise, cinnamon stick, and tangerine zest. Bring to a boil, then reduce heat, cover, and simmer for 3 hours. Remove from heat, add eggs, and let steep for at least 8 hours.