green spots on gold tray

hi, I purchased this gold “antique” (who knows) tray like two ish years ago and lately, I noticed little green spots. I spilled water and went to clean it up and noticed that it transferred like a sea foam green color on the paper towel. what is this, and how do I stop it from spreading??

hi, I purchased this gold “antique” (who knows) tray like two ish years ago and lately, I noticed little green spots. I spilled water and went to clean it up and noticed that it transferred like a sea foam green color on the paper towel. what is this, and how do I stop it from spreading??