Retrobright

Retrobright (stylized as retr0bright or Retrobrite^[1]) is a hydrogen peroxide-based process for removing yellowing from ABS plastics.

A TRS-80 Color Computer showing significant yellowing

The same computer after treatment, showing yellowing largely reversed

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]

History

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]

Composition

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:

• A hydrogen peroxide solution.^{[8][unreliable source?]} Hydrogen peroxide-based hair bleaching creams available at beauty supply stores can also be used, and are viscous, allowing them to be applied with less waste (especially to large pieces such as computer panels or monitors).^{[9][10][unreliable source?]} The cream must be carefully applied and wrapped evenly with plastic wrap to avoid streaks in the final product.^[11]
• Approximately 1 ml per 3 liters (1 part in 3000 by volume, alternatively 1⁄4 teaspoonful per US gallon) of tetraacetylethylenediamine (TAED)-based laundry booster (concentrations of TAED vary).
• A source of ultraviolet light,^[8] from sunlight or a UV lamp.^[7]

Xanthan gum or arrowroot can be added to the solution, creating an easier-to-apply gel.^{[citation needed]}

Alternatives

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]

A simpler but slower process involving merely exposure of the yellowed plastic to bright sunlight has been described, variously called 'Sunbrighting' or 'Lightbrighting'. This has both empirical evidence of effectiveness and the theoretical backing of some published scientific literature, which emphasises exposure to strong visible light while minimising ultraviolet exposure.

Effectiveness

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]

Similar processes

The usage has also expanded to other retro restoration applications, such as classic and collectible sneaker restoration.^[15]