Last Updated on October 4, 2021 by Dave Farquhar
I heard earlier this year that you can retrobright without chemicals, using only sunlight. I haven’t heard of a lot of people trying it. But I had a yellowed disk drive, and it’s summertime, so I decided to give it a shot.
A few people experimented with retrobright without chemicals in 2019, then the idea kind of faded away. I decided to try it, and found it works surprisingly well.
How retrobright works
Retrobright has long been a mystery. For a long time we thought it was due to bromine, included in plastics to act as a flame retardant, yellowing due to some combination of ultraviolet light, heat, and age. But we’ve recently learned it’s oxidation. Yes, like rust.
What retrobright does is bleach the oxidation back out. You can do it fast with combinations of certain chemicals (usually hydrogen peroxide, though some others can also work) along with full spectrum light and heat. But that’s not the only way.
Over the years people have found multiple combinations that work. High-concentration hydrogen peroxide in a huge tub on a sunny summer day is the most popular combination. But there are people who have used artificial light, such as grow lights or even modified LED bulbs. I’ve also seen people use just heat, without any light. The combination of light and peroxide seems to work best, and heat speeds up the reaction, but what exactly it’s doing to the plastic isn’t completely clear.
Retrobright with just the sun
It’s June, and I’m working from home, so I decided to try retrobright with just the sun. I had a very yellow Apple II disk drive. It works, it just looks bad. I also don’t have much emotional attachment to it. Commodores are my thing. I used Apple IIs a little bit in high school, but I was indifferent to them then, and today I’m just mildly curious about them. That disk drive was the lowest-risk item I had with yellowing to experiment on.
How well it works depends on how much sun you get. I’m in Missouri. We get some sun, but not like southern California or Florida, where I’ve heard of this working well.
My experience with retrobright without chemicals
I set the drive out on a Sunday morning. It wasn’t early enough to get all the sun that day had to offer. I took a photo beforehand. After a partial day in the sun, it seemed like the yellow faded a little on the side that got the most sun, but I couldn’t tell if it was my imagination or not.
On Monday, I set it out around 7:30. The morning sun isn’t very intense, but why not use what we can get? It got over 12 hours of sunlight. I set a different side facing the direction of the most intense sunlight, and that side seemed noticeably brighter after 12 hours in the sun. The rest of the drive didn’t seem all that affected. Maybe a little.
I took it out earlier on Tuesday. Out at 6:30, back in at 8:30.
I think the yellowed surfaces need at least 12 hours in the sun, if not a bit more, to fade. But if I can get a side a good 12 hours in the sun, that side does look noticeably better afterward. The ugly nicotine-colored patina fades away, leaving the plastic something much closer to its original color. That first 12-24 hours gives the most improvement, but more time gets you closer to the original color.
I expect it’s faster if you’re closer to the equator, and slower the further from the equator you are.
What about overcast days?
I got five days in a row that were clear, during the longest days of they year. If I’d been willing to get up at 5:30, I could have had 15 hours of sunlight. Of course the light isn’t very intense at sunrise and sundown. But I was able to get more than 12 hours of intense light.
On the sixth day I put the drive out, it was only partly sunny. The drive didn’t improve as much that day. Now, after five days, the drive had less improvement to gain. Was it worth it? It’s not like it cost me anything. How long does it take to set a disk drive on the porch in the morning and bring it back in at night?
Don’t put it out in the rain of course. But as long as it’s not raining, I think it’s worth putting a yellowed machine out, if you have one.
How long does the improvement take?
I noticed the biggest improvement after Day 2. Then from that point onward, I pointed the yellowest side toward the sun. I noticed improvement when I brought the drive in for the evening, at least on the side I aimed at the sun. The rest of the drive didn’t get so much improvement. Some days, the color would be inconsistent on the side that got the most sun. Placing it in the sun again with that side aimed at the sun leveled it out the next day.
There’s a square patch on the drive that was covered by a label, preserving the original color. After Day 6, that patch was still visible, but was starting to show inconsistencies in the area around that patch. Six days in the Missouri sun in June was enough to get the drive close to its original color, but not quite there. The estimates I’ve heard that it can take up to two weeks seem plausible.
But it depends on the plastic. Apple plastics take longer. My Amiga 500 improved in just a few hours.
Why not use chemicals to retrobright?
Chemicals make retrobright go much faster. No question. But it’s much easier to set it out on the patio in the morning. It’s slow, but it’s completely passive, and it’s free. I just have to keep an eye on the weather. But in this case, I had a week that was supposed to be clear, which made it easy. Just set it out first thing in the morning, and bring it in at dusk. I didn’t even have to take anything apart.
And chemicals have disadvantages. There’s little question it makes the plastic more brittle. A week in the sun doesn’t seem to have that same effect. It’s a slower, gentler process. Plastic does deteriorate in the sun, of course, eventually. But that takes years, not days.
The other disadvantage is the possibility of it going bad. I’ve heard of it with Atari systems more than others, but sometimes when you put a system out to retrobright, you get splotchy, uneven results. A second round usually doesn’t improve it, so then you have to paint the system. Using sunlight is a lower-risk process. If the plastic looks uneven after a day in the sun, putting it out for another day has cleared it up, in my experience. And when I’ve observed uneven results, it’s been in areas where I had to use a harsh cleaner to remove severe marks on the surface.
Even slower retrobright indoors with LED lights
Some people believe LED lights impede yellowing, and I’ve even heard of people modifying LEDs to emit bluer light and use those directly for retrobright.
I have some computers, including a Commodore VIC-20 and an Apple IIc, that were slightly yellow, but I hadn’t done anything about it yet. I had them hanging on my wall in my home office, on picture ledges. I hung them up in October, and one day in February I noticed both of them looked a lot less yellow. I use LED lights in the office. So it seems five months of getting blasted with LED light for about 9 hours a day lightened them up.
I thought I was imagining things, but there’s part of the Apple IIc that’s covered by the lip of my picture ledge, and it’s noticeably yellower than the rest of the machine. I remember the whole machine looking like that when I first pulled it out of storage.
So if you’re patient, you might want to try just keeping your systems out where they’re exposed to light, and use LED lights in the room. I’m going to set out some other yellowed machines under the same conditions and see if they change.
And for what it’s worth, that Apple disk drive I retrobrighted in the sun hasn’t re-yellowed at all. I keep it in the same room.
Is it the LEDs, or a combination of LEDs and lack of sunlight?
I’ll caveat all this by saying there’s also no sunlight coming into this room. The window gets really direct sun during part of my workday and I find the glare distracting, so I have blackout curtains in the room. And during the coldest months, I keep them closed to keep the room warm. So the absence of sunlight coming in through the window may also be a factor.
Sunlight coming in through the window is almost certainly a factor in plastics yellowing.
If my experiment doesn’t work, I should have a pretty good idea by June. And I’ll have lots of sunlight to work with again at that point.
David Farquhar is a computer security professional, entrepreneur, and author. He started his career as a part-time computer technician in 1994, worked his way up to system administrator by 1997, and has specialized in vulnerability management since 2013. He invests in real estate on the side and his hobbies include O gauge trains, baseball cards, and retro computers and video games. A University of Missouri graduate, he holds CISSP and Security+ certifications. He lives in St. Louis with his family.