It’s a tale nearly as old as computers themselves. You pull your trusty old video game console or vintage 1980s computer and it’s yellow, greenish, or some combination there of instead of the gray or beige it once was. What gives? Why does your old tech turn yellow? And further, what can you do about it?
Dear How-To Geek,
I’m helping my parents purge decades of stuff packed in their attic before they downsize their house. In the process I’ve found all sorts of old tech gear like my Super Nintendo and my old Mac. I’m really curious about something. Some of the old stuff looks pretty much like I left it. Some of it has yellowed, almost like it was left in a smoker’s office for decades. Some of the objects, like a few of the Super Nintendo games only yellowed on one side! That’s super weird, half the game cartridge is the original grayish purple color I recall and half of it is a really yellow color.
So I have two questions. What causes the yellowing, and is there anything that can be done about it? I’d guess it was sunlight exposure, but these devices were normal colored when they went into a box in the attic and they didn’t sit in sun all these years. I don’t need my Super Nintendo system to look brand new or anything but it would be nice to clean it up in case I feel like displaying it on an office shelf. What do you think?
Stained Up SNES
Ah yes, the mystery of the every yellowing electronics case. As you’ve discovered it’s not an every time thing (and sometimes, even, two halves of the same device will yellow at different rates or one won’t yellow at all). So what does cause the yellowing and what can you do about it?
Why Old Computers and Consoles Yellow
In nearly every case it’s flame retardants. Although plastics can yellow in the absence of flame retardant chemicals, the chemicals accelerate the process when exposed to heat, oxygen, and ultraviolet rays.
In the case of old desktop computers, especially old Macintosh machines with their plastic beige cases, the culprit is typically (but not always) plain old UV exposure. It doesn’t have to be UV exposure from direct sunlight either as the majority of fluorescent office lights are unshielded and shine lots of UV light down inside even windowless offices. The flame retardants used in most old Mac cases were fairly heat stable and short of getting blasted by 12+ hours a day of natural or artificial UV exposure they tended not to yellow too badly.
The plastics used in early Super Nintendo units, however, had a terrible flame retardant mixture that yellowed as a result of the oxidation caused by the heat of the machine itself (let alone any heat in the environment). Your Super Nintendo might have gone into the attic in mint condition but just being in a hot attic for years would be enough to yellow the plastic significantly. As for why you’ve found games in your collection that are half normal color and half yellowed, that one’s easy.
When the problem with the Super Nintendo plastic mixture was discovered there were already significant stocks of SNES console shells and cartridge shells already molded and ready to use. When the new formula was rolled out some of those old leftover old-formula pieces ended up mixed in with the new ones as they ran through the production stock. As they depleted the old stock the problem of the yellowing plastic vanished (but not without more than a few Franken-build consoles and cartridges ending up with different formulas).
We’re sure you’ll find the science of it all pretty fascinating (an assumption we make based on the fact that you cared enough about a novel and geeky topic to write in and ask about it) and we’d highly recommend checking out a rather detailed look at the reasons behind the yellowing at Vintage Computing and Gaming.
What You Can Do About It
When it comes to removing the yellow there are quite a few techniques out there but they all revolve around one of two core methods: removing the yellowed plastic via mechanical action or removing it via chemical action.
Some people use ultra fine sandpaper or melamine sponges to sand away the very surface of the plastic and remove the yellowing. This works for very light yellowing and plastic types where the yellowing hasn’t penetrated very deeply into the plastic. Unfortunately it only works by removing the actual yellowed plastic so if the item in question is very old and/or the yellowing has deeply penetrated the shell, you risk significantly altering the body of the device to restore the color.
The other method, chemical removal, relies on using bleaches to attack the yellowed molecules in the plastic and restore the color. This method is best for very old and very yellowed plastic as it gets right into the structure of the plastic and does a very thorough job. There are some downsides, however, as it’s possible to actually lighten the plastic lighter than it’s original shade (a feat that’s impossible when sanding down the plastic via mechanical action) and some plastics may become more brittle after exposure. A common recipe used by computer and console restorers is known as Retr0Bright. In addition to the actual recipe the Retr0Bright site has some great bits on the science of the yellowing process and how to reverse it. The image above, courtesy of their wiki, shows what a difference the solution makes on an old Commodore shell after 8 hours of soaking.
Before we leave the topic, let’s talk about what you need to do after you’re done restoring the color. Whatever technique you ultimately decide on you will need to coat the shell of your device or cartridge in a UV protectant (such as a clear matte UV-protectant spray paint) or else the yellowing process will just start all over again and within years you’ll have a yellow case. Don’t spend a whole weekend scrubbing and soaking your cases just to leave them exposed; seal the plastic up and enjoy that showroom-new color for decades.
Have a pressing tech question? Brand new or retrorific, we’ll do our best to answer it; shoot us an email at email@example.com.