I got a G1 lot that had a Slugslinger. He was the rarest of the TFs in there but also the one in worst shape. He had yellowed badly.
Here he is next to another G1 from that lot, Silverbolt, who kept his white color:
I didnt know what to do. Transformer forums were suggesting a bunch of stuff from sanding the yellow off (bad idea since you risk destroying your rare toy) to dumping the transformer in a vat of hydrogen peroxide for 3 months(also a bad idea since everything will rust).
Hydrogen peroxide was the best option strictly for bleaching but nothing above 3% concentration is sold to consumers and even if you found a high percentage (12% is needed if you dont want to wait 3 months) you would need a bunch to submerge your figure in. Slugslinger has quite the wingspan. So it looked impossible.
However, there was a whole bunch of info on how to remove the yellow colouring from old white mac computers (because apparently, that too is soemthing people collect). Since Computers have large surfaces, dumping them in hydrogen peroxide would not work. You would need so much. So instead, you would need to turn the hydrogen peroxide into a cream to spread over it.
Lucky for us, such peroxide creams to exist for bleaching hair, and you can buy the heavy stuff over the counter at any drugstore or beauty salon. And when you look at the ingredients, it's just water and hydrogen peroxide and some thickening agent to spread it, so it's perfect. By being able to spread it, you dont hae to dunk the figure in a solution, so it wont be all wet for days on end and wont rust. You can also choose which parts of your figure to coat in the cream.
Once the cream is applied, put a saran wrap over the figur so that the cream does not evaporate. UV rays are responsible for the chemial reaction which turns figures yellow, and thus they are also needed for it's reversal. I have a black light, so I just posed it near my figure so that the figure would bathe in the UV rays for 36 hours. The plastic wrap made the hydrogen peroxide cream stay the whole time.
36 hours laters, I removed the plastic wrap and cleaned my figure in soapy water to remove any hydrogen peroxide residue.
It became a beautiful neutral gray. Here it is ready to be given some new decals.
Just to show what it looked like before again