Plain metal coin engraving seems to have no color accents, try deep engraving and then filling in the colors to make your work pop!
Use nail polish remover sanding strips to polish the dust on the gold coins and use alcohol wipes to clean the surface of the gold coins to keep them clean.
Choose your favorite nail polish, if you don't have the right color you can try mixing it yourself. You can also buy some special flowing nail polish to fill in the color. Fill in the color and use the violet light to irradiate for 60s
Don't touch the processed gold coins immediately to prevent high temperature burns.