Here's why:
* Durability: Both materials are strong and resistant to wear and tear, ensuring the ball doesn't break down or rust inside the bottle.
* Inertness: Neither material reacts chemically with the nail polish, keeping the formula intact and preventing any unwanted discoloration or changes in consistency.
* Smoothness: The ball is smooth and round, allowing it to easily mix the polish without scratching or damaging the bottle.
So, the next time you shake your nail polish, you'll be using a little piece of stainless steel or glass to get that perfect, smooth finish!