De-yellowing (Retrobrighting) plastics in computer gear: Is the Sun all you need?


Yellowed cases give our ancient computers “character”, right?  Err...that's debatable. I expect most collectors (including me) would rather have them looking like they did out of the box all those years ago.  Thankfully since around 2009, variations on a “Retrobright” remedy have been available, most of which involve using hydrogen peroxide, UV light and laundry activators to reverse the effect. I’ve experimented with this myself with good results. Disappointingly, I’ve also found the Retrobrighted items can re-yellow over time even though stored in almost complete darkness! 

One of the hazards of using hydrogen peroxide and laundry activators for de-yellowing is the damage to the plastic that can occur. For instance coloured cases can show a spotty “bloom” if the retrobrighting process is overcooked (i.e. too long a exposure or too much peroxide or activator).  It's also a relatively messy process and the ingredients can be hard to source.

Recently, discussion forums and videos have suggested sunlight alone is all that’s needed for yellow in the plastics to fade.  This seemed to be a safer and less messy solution to the yellowing problem. At the height of a New Zealand summer, I decided to give it a go.


I selected four items that clearly showed yellowing.  An Atari XE130 (actually more a greening than yellowing!), an Acorn 400 keyboard (cheese-yellow!), a VIC-20 and a Mac 128.  The Atari and VIC-20 had been retrobrighted by conventional means in 2009 however, both had returned to their yellowed states (see the links above).

The "sunbathing" happened over a week in early February (our mid-summer). Two days of that week were cloudy and the items were not put out.  However, five days were fine and on those days the units stayed out for about 6 hours each day.  Average temperature was around 26 degrees C or so.

The Mac 128 was put out towards late February.  It had about the same exposure, but temperatures were a little cooler at 22 degrees or so, and the sun just a little lower in the sky. 

The photos show what happened.  I tried to take the photos comparing each unit in more or less the same place and under the same lighting conditions. My camera made some automatic decisions on exposure though as you can tell from the background. However, the photos pretty much show the comparative degree of yellowing (or non-yellowing) visible to the eye.

(i) Atari XE 130

This was a great result.  The machine went a long way towards returning to its original colour.

Photo 1. Atari XE 130 before 5 days in the hot sun

Photo 2. Atari XE 130 after 5 days in the hot sun

(ii) Vic-20

Another great result.  From yellow to white.

Photo 3. VIC-20 before 5 days in the hot sun

Photo 4. VIC-20 after 5 days in the hot sun

(iii) Acorn 400 keyboard

Amazing!  The case went from cheese yellow to a pale cream. It's no longer an embarrassment!

Photo 5. Acorn 400 Keyboard before 5 days in the hot sun

Photo 6. Acorn 400 Keyboard after 5 days in the hot sun

Photo 7. Area of the keyboard showing original colour where label had been – before 5 days in the hot sun

Photo 8. Area of the keyboard showing original colour where label had been – after 5 days in the hot sun

(iv) Mac 128

The result here was not quite as dramatic.  There WAS some fading of the yellow…from cheese-yellow to a cream-yellow.  The result can be seen in these two before-and-after flash photos.  The flash tends to overplay the yellowing somewhat.

Photo 9. Mac before 5 days in the hot sun (taken with a flash)

Photo 10. Mac after 5 days in the hot sun (taken with a flash)

I wrapped the exercise up after a week both times because no further deyellowing seemed to be taking place. The deyellowing never seemed absolutely complete, although it’s hard to ascertain this, as I don’t have original pristine units to compare my ones with.  The VIC020 faded to a very, very light cream colour, but not back to completely white.  The Atari XE 130 seemed to still have a "ever-so-slight" tinge of green in a corner, and its spacebar was still dark. The Acorn keyboard didn't quite get back to that original colour as revealed in that area where a sticker used to lie.

However, all results were good enough!


Sunlight in New Zealand has very high UV levels.  I’m satisfied that sunlight alone (at least in a NZ summer) can indeed de-yellow these plastics, although the process seems to plateau before items are fully deyellowed.

I felt that heat played an important role here.  I’m wondering if the less-than-impressive Mac result reflects the fact that the days were getting cooler, and the sun was just a little less intense.

Why does sunlight only work?  Nowadays there seems to be a lot of contradictory information/debate about what causes the yellowing process in the first place, the role of hydrogen peroxide, activators and UV light in deyellowing, and why yellowing sometimes returns. Do some Google trawling and you'll see what I mean. I’ll let those more qualified than me continue to debate this.  Certainly, the UV in sunlight is known to bleach plastics, flooring and fabrics (i.e. turn them pale), so I suspect that is what is going on here.

Long term exposure to sunlight does weaken plastic. Just consider those ubiquitous white garden chairs and what condition they are in after a number summer seasons.  They become brittle.  Is it safe then to leave computers in the sun for a week or so?  I’m happy to take that chance.  Five days in the sun is a relatively short exposure and I didn’t notice any obvious weakening of the plastic. Certainly sunbathing is likely to be LESS hard on plastics than full-on retrobrighting with chemicals.

It’s a method I’ll now use for my remaining yellowed items.  Roll on the next New Zealand summer.  However, it will be interesting to see if this deyellowing effect is just temporary like the last one.

Terry Stewart
20th March, 2020


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