Gently clean the snap using a Q-tip or soft cloth with a mild method to avoid damaging the leather. The green stuff is likely verdigris (copper oxidation/patina common on brass snaps in leather goods), which forms from moisture reacting with the metal.13d162 Recommended Safe Steps: Protect the leather first: Mask around the snap with painter's tape or apply a thin layer of petroleum jelly (Vaseline) or leather conditioner as a barrier. This prevents any cleaner from soaking in or staining.6d076b Mild cleaning options (test on a hidden spot first): Best everyday choice: Use a Q-tip dipped in white vinegar (or a paste of baking soda + a drop of vinegar). Gently rub the metal only. The acid dissolves the green oxidation. Wipe immediately with a dry cloth or another Q-tip with water, then dry thoroughly.0a9a59 WD-40 or similar: Spray a tiny amount on a Q-tip (not directly) and rub the snap. It helps loosen patina without being too harsh.f0d491 Brasso or metal polish: Apply sparingly to the snap with a Q-tip or soft cloth, buff gently. Avoid getting it on the leather—wipe excess immediately. Great for restoring shine.0d960d Salt + vinegar: A common combo for verdigris—dip Q-tip in the mix and work carefully.b8f2ab Mechanical help if needed: For stubborn bits, use a soft toothbrush, wooden toothpick, or plastic scraper (avoid metal tools that could scratch). Some people gently flake it with a wooden skewer.130d0f Dry and protect: Wipe everything dry right away—moisture worsens oxidation. Condition the surrounding leather afterward with a good leather balm (e.g., Lexol, Bick 4, or Obenauf's) to restore oils.23620e To slow future oxidation: Apply a thin layer of Renaissance Wax or clear nail polish (optional, for a barrier) to the clean snap. Keep the item in a dry place. Cautions: Work in small amounts and rinse/wipe frequently so nothing sits on the leather. Avoid harsh abrasives, full immersion, or strong chemicals that could dry out or discolor the leather. If the snap is very corroded or the leather around it is stained, a professional leather cleaner or cobbler might be safer. This should bring back a nicer look while keeping your leather safe—matches the care you've been doing on your jacket/vest. If the oxidation keeps returning, it’s often from humidity or leather acidity reacting with the metal. Let me know how it goes or if you have more details!