Retrobright (stylized as retr0bright or Retrobrite[1]) is a hydrogen peroxide-based process for removing yellowing from ABS plastics.
Yellowing in ABS plastic occurs when it is exposed to UV light or excessive heat, which causes photo-oxidation of polymers that breaks polymer chains and causes the plastic to yellow and become brittle.[2]
One method of reversing the yellowed discoloration was first discovered in 2007 in a German retrocomputing forum,[3] before spreading to an English blog where it was further detailed.[4][5][6] The process has been continually refined since.[1]
Retrobright consists of hydrogen peroxide, a small amount of the "active oxygen" laundry booster TAED as a catalyst, and a source of UV.[7]
The optimum mixture and conditions for reversing yellowing of plastics:
Xanthan gum or arrowroot can be added to the solution, creating an easier-to-apply gel.[citation needed]
Sodium percarbonate may also be used by dissolving it in water and following the usual steps for hydrogen peroxide, as it is sodium carbonate and hydrogen peroxide in a crystalline form.[8]
Ozone gas can also be used for retrobrighting, as long as an ozone generator, a suitable container of sufficient size and a source of UV are available, but can take longer than other methods.[8]
The long-term effectiveness of these techniques is unclear. Some have discovered the yellowing reappears, and there are concerns that the process weakens and only bleaches the already damaged plastic.[12][13][14]
The usage has also expanded to other retro restoration applications, such as classic and collectible sneaker restoration, where it is referred to by collectors as "sole sauce".[15]