Copper is fickle and it has taken me about 50 of these 4x4 engravings to get the settings right. Imaged were created with the AI feature in the XCS software. XCS File Included Below.
Sand well and degrease with a metal degreaser. I use the degreaser from sculpt Nouveau. Any grease from your fingers or other source will stop the laser from marking properly.
I have tried all the laser sprays and brilliance works best on copper. You can mark copper without spray, but you will be much better results with it.