Well, this is how it how it goes most of the time when using the hydrogen-peroxide cream technique. However, I used the technique of submerging the plastic keycaps into 3% hydrogen peroxide but for experimentation purposes I only used enough to cover the keycaps half way and this is the strange result: The Keycaps are gray from factory as you can see from the keycap on the right. However, the keycap on the left was left halfway submerged in the hydrogen peroxide and where there was no hydrogen peroxide, it became white. This was after less than 3 hours under the sun.
However this is how it looks after 4 hours under the sun and completely submerged under hydrogen peroxide:
Left: how it looked before retrobrighting it, right: after completetly submerging it under 3% hidrogren peroxide for 4 hours under the sun.
It didn't went white being more time under the sun and with more hydrogen peroxide (Its factory gray color remained intact).
Tips:
- Avoid having air bubbles that can lift whatever you are retrobrighting.
- Check after 3 hours if it's ready because it can overbright the plastic.