This is something I've been interested in for awhile, I had success whitening and removing mold spots on white and yellow ponies using RemoveZit but hydrogen peroxide seems to have wider affect and overall easier to use, although it's risky and has its share of pros and cons.
This method has been used successfully among Transformers and GI Joe collectors, here's instructions written by kup
- Get a clear glass jar with a seal tight lid (I use an mayonnaise jar like this one with the label removed)
- Buy a Jar of Hydrogen Peroxide with at least 6% w/v from a Pharmacy or Super Market (Pharmacy is more reliable)
- Fill the glass container with the appropriate volume of Hydgrogen Peroxide depending on the size of the yellowed piece.
- Once the piece is submerged, expose the jar to sunlight for a few days (oh the irony! ) until the plastic color is 'corrected' to your satisfaction. During this process you will see thousands of small bubbles covering the surface of the plastic - This is the Hydrogen Peroxide at work.
Advice: Try not to have too many pieces of plastic in one jar. The crowding of pieces slows the process as they shield each other from sunlight.
Note 1: Some plastics are more successful at regaining their color than others but something that seems consistent from my experience is that there is always a considerable improvement. It seems that different plastic types regain their colors at different rates - The level of yellowing is also a factor in the length of the submerged time period.
Warning: Hydrogen Peroxide is corrosive to metal. However from what's available in retail, the level of concentration is so low that it seems negligible. I have not seen any corrosion in metal rods and pins joining plastic parts even after being submerged for a couple of weeks.
Warning 2: Although most painted parts will not be affected by the Hydrogen Peroxide, there is documentation that some do. Toys with painted detailing which fades with exposure to the Hydrogen Peroxide includes: AM Megatron (Purple).
VERY IMPORTANT WARNING: Hydrogen Peroxide is also toxic so try to avoid exposing your skin to it. Try to use gloves and if it goes on your skin, wash the affected area immediately.
Note 2: I have used this process in at least half a dozen toys without any ill effects to the plastic even after more than a couple of weeks submerged. It's been about a year's time since my first attempt and the plastic of the toy in question is still fine. However regardless of success, the plastic is still vulnerable to yellowing again if exposed to UV rays because that's the nature of the plastic.
Disclaimer: Although I have been successful with several toys using this procedure and I have not observed any ill effects on the plastic - there is no guarantee that it will work for you and there is always the possibility that some plastics may not react well to the Hydrogen Peroxide so proceed at your own risk.
Notes specific to Grotusque:
Grotusque has a big pin that joins his legs together - You cannot remove this without breaking the plastic. The best thing to do so that his yellowing can be fixed is to separate the whole 'legs' assembly and remove every single screw that you can find so that you don't have to unnecessarily expose them to the HP. Unyellowed plastic does not seem to be affected by the Peroxide but still try to separate as many 'healthy' pieces from the assembly as possible.
The top half of the body is easy to separate so if its just the shoulder, you shouldn't have any problem removing the affected piece.
Here's amazing before and after pictures taken by catilla
Many more pictures and information can be found here:
I'm thinking of testing this method on a few baits, but would like to know first if anyone tried it on MLP?