Ok... The results are in...
After a 10 hour soak in the Retr0Bright mix and under the "BlackLight", this time there has been quite a difference...
Results of a very badly yellowed VIC20 case (right half only)
Result of some very yellowed A1200 key caps
Notes:
The N key is how all keys looked originally ...
The 9 key is taken from a brand new keyboard from AmigaKit for comparison purposes...
While there has been quite a difference the results aren't the best, could be the mix wasn't strong enough or due to lack of not using direct sunlight (bit of a problem here, cos we only had about 1 hour of sunlight today).
Myself I reckon I need to make a better "paste" as the foaming action was very patchy and inconsistent. It's quite difficult to get the Oxy powder to dissolve properly without watering it down too much and thus weakening the whole solutions strength.
Having said that I did choose the worst cases I could find (pun intended). Going to try mixing up another batch and try this time to get a more consistent foaming action and redo the above pieces and see if things can be improved a wee bit...