What is this cameo finish?

by Lauren
(Fayetteville, AR )

Hi! I'm a jewelry designer who redesigns vintage jewelry. Recently, I created a ring from a vintage cameo. My client, who is a hairdresser & washes a lot of hair, washed with the ring on and the brown finish on the cameo washed away. She is wanting to recreate this look. What can I use to create the brown contrast lines on the white cameo?

Thank you!!