Bromine flame retardants turn ABS plastic yellow over time. Retrobright reverses some of it, but the process is slow and easy to overdo.

What we used

• Hair-developer cream at twelve percent, applied thin.
• Cling film to stop it drying out.
• A turntable made from a lazy Susan so the sun hit evenly.

Check every hour. The difference between restored and marbled is about forty minutes.

Workshop whiteboard, June

After three sunny weekends the top case is close to its original grey. The keys, done separately, are a shade lighter, which we have decided to live with.