Foolproof? No. Likely to work? Yes.
- Hand wash the case well.
- Remove badges and other things that don't need bleaching.
- Buy peroxide hair developer cream, it's on Amazon: https://www.amazon.com/Salon-Care-Stabilized-Consistent-Predictable/dp/B0BZTKTFQC/
- Apply the cream evenly, not too thickly.
- Expose the treated case parts to UV light. Time depends on UV strength.
- Fully wash the treated case parts. Check for areas that need another round of exposure. If needed, go to (4).
Some people prefer sunlight. Wrap the case in plastic wrap to prevent the cream from drying out.
I prefer using a UV box because I've had inconsistent results from sunlight. The UV box resolves this. I made one with a large tote lined with reflective material. LED UV lights are wrapped around the inside sides and on the top. With this I do not cover the parts with plastic wrap, I just leave them in the box for 24 hours then check. I wash all of the cream off, check everything, and if necessary treat again exactly the same way.
For items that are not badly yellowed, I try them in the UV box *without* peroxide developer, but this takes much longer — one item took a full month.
