Stainless is one of the Achievements a player can accomplish in Audiosurf. To attain it, the player must earn Clean Finish and score high enough to receive a Gold Medal three times in a row. This achievement can be earned with any character, and there is no requirement for it to be the same song played three times nor three different songs. Use character bonuses to your advantage when attempting this achievement. Stealth gains a 30% bonus, Clean Finish, which is already mandatory to this achievement, earns you a 25% bonus. Also, enabling Ironmode gives a bonus.
The easiest way to earn this achievement is to play one of the Eraser characters, and play 3 slow songs which last for a short period of time.