Don't do the "sun brighting" method, you're just further damaging the plastic in exactly the same way that caused it to yellow in the first place exposing the plastic to more UV & heat in an uncontrolled environment for far longer than is necessary, which is generally not good for it. The fact that it goes white-ish again is immaterial. Even if you're retrobrighting in direct sunlight, using peroxide to aid the process allows you cut down the exposure time by a large margin.

The peroxide method does work, but there's evidence around that it's not a very permanent fix. It may or may not damage the plastic again. Personally I wouldn't do it on something especially hardened or brittle. Late '90s plastics are generally fine, mid '80s - proceed with extreme caution. If little clips are breaking off or corners are crumbling when you open it up, best to leave it be.

This isn't a well understood process; lots of enthusiasts are trying it & posting results, which is great, but that doesn't equal a rigorous scientific study of what's actually going on.

There is a risk of brittling, so I'd advise against retrobrighting tiny plastic parts, particularly older than 25-30 years old.

However, when it comes to case faceplates, CD-ROM faceplates, mice cases and keyboards, you should mostly be fine.

just accept that stuff gets yellow with age?

Nah. In my opinion, color is what separates museum-level machines from simple trash.

xjas wrote on 2020-01-08, 20:43:

Don't do the "sun brighting" method, you're just further damaging the plastic in exactly the same way that caused it to yellow in the first place. The fact that it goes white-ish again is immaterial.

This is not true and I can actually provide you with a lot of proof that it's not sunlight that causes yellowing.

For example, even items left to rot in nature do not yellow like items exposed to sunlight indoors: https://www.youtube.com/watch?v=K3q1gmte_CY

And anectodally, a lot of items I had in a dark storage with no sunlight whatsoever have yellowed over time, inexplicably by conventional 'Sun causes yellowing' wisdom.

It might be that a certain spectrum of light (which may be a problem exacerbated by windows filtering sunlight in some way) actually accelerates the process, but it in no way causes it. It is, in my mind, almost definitely more related to temperature and humidity.

Do sunbrighting. It works, and I haven't had a single item go brittle or break.

Ok, I adjusted my post. However, I wouldn't unconditionally recommend someone 'do sunbrighting' as a blanket fix. Especially on a machine they're nervous about damaging further already. I think caution is warranted.

If you have some stuff you've sunbrighted and it worked really well, please post up pictures and tell us how long you left it out for. So far everything I've seen are examples that got "whiter", but didn't look right - more like they'd been left out in the desert and started to deteriorate.

Gonna be a prick and quote myself, because I think this is the important bit of the statement I was trying to make:

xjas wrote on 2020-01-08, 20:43:

This isn't a well understood process; lots of enthusiasts are trying it & posting results, which is great, but that doesn't equal a rigorous scientific study of what's actually going on.

Oh sure, let me share my experience with sunbrighting:

This is Day 0 for a keyboard and faceplate:

This is the end of Day 1 (1 full day of spring sun)

The keyboard frame is de-yellowed somewhat but still not white. There is little progress on the faceplate.

This is the end of Day 2 (2 full days of spring sun) for the same duo:

You can see that the keyboard frame is nearly perfect white and the faceplate has shed off some of its yellowing (compare with the original color in the rectangular sticker mark on the faceplate).

I actually sunbrighted these two for one more day and the keyboard got pristine white but the faceplate was still somewhat yellow, but I stopped at that point. I can't seem to find a photo of the last day, unfortunately.

I would like to know if there is a way make things less yellow without sun. I would like to make case face plate less yellow and not have to wait until summer to do so.

Baoran wrote on 2020-01-09, 11:54:

I would like to know if there is a way make things less yellow without sun. I would like to make case face plate less yellow and not have to wait until summer to do so.

Yes, you can use hydrogen peroxide mixed with water, submerge the parts and heat them to around 50C or so, if you have a thermostate heater of the required size.

8-bit Guy has a video about this method.

xjas wrote on 2020-01-08, 20:43:

Don't do the "sun brighting" method, you're just further damaging the plastic in exactly the same way that caused it to yellow in the first place exposing the plastic to more UV & heat in an uncontrolled environment for far longer than is necessary, which is generally not good for it.

These systems were used and exposed to sunlight for years when they were new, especially if used in class rooms or offices. While I understand your point, exposing them to sunlight for another few days won't hurt them much. While plastics can get brittle when heavily exposed to sunlight, this is a process that takes months or even years, not days. And it's also not caused by the sunlight itself but by heat, which makes the softener evaporate. UV light has little to do with it. The sunlight that reaches the Earth only contains UV-A and UV-B (UV-C won't pass the atmosphere) and these only have an effect on the direct surface. They are too weak to get deeper into plastics.

appiah4 wrote on 2020-01-09, 06:36:

[...]
And anectodally, a lot of items I had in a dark storage with no sunlight whatsoever have yellowed over time, inexplicably by conventional 'Sun causes yellowing' wisdom.

It might be that a certain spectrum of light (which may be a problem exacerbated by windows filtering sunlight in some way) actually accelerates the process, but it in no way causes it. It is, in my mind, almost definitely more related to temperature and humidity. [...]

I had similar suspections in the past, too... does anyone happen to have a well-founded explanation for that? Maybe together with a recommendation on how to store hardware in conditions that will prevent yellowing?
Once I had a TFT screen from the early 2000s stored away in a basement for a few years, so no sunlight exposure at all, and it came out much more yellowed than it was before. But I don't remember the conditions regarding temperature and humidity in that particular basement.

The room where I currently store my retro hardware is in a basement as well, temperature is between 11°C (winter) and 17°C (summer), humidity is around 60-70% in the winter and often well above 80% during summertime. While I would suspect that lower temperatures are generally a good thing, the quite high humidity might be harmful?

gex85 wrote on 2020-01-09, 12:58:

I had similar suspections in the past, too... does anyone happen to have a well-founded explanation for that? Maybe together wit […]
Show full quote

appiah4 wrote on 2020-01-09, 06:36:

[...]
And anectodally, a lot of items I had in a dark storage with no sunlight whatsoever have yellowed over time, inexplicably by conventional 'Sun causes yellowing' wisdom.

It might be that a certain spectrum of light (which may be a problem exacerbated by windows filtering sunlight in some way) actually accelerates the process, but it in no way causes it. It is, in my mind, almost definitely more related to temperature and humidity. [...]

I had similar suspections in the past, too... does anyone happen to have a well-founded explanation for that? Maybe together with a recommendation on how to store hardware in conditions that will prevent yellowing?
Once I had a TFT screen from the early 2000s stored away in a basement for a few years, so no sunlight exposure at all, and it came out much more yellowed than it was before. But I don't remember the conditions regarding temperature and humidity in that particular basement.

The room where I currently store my retro hardware is in a basement as well, temperature is between 11°C (winter) and 17°C (summer), humidity is around 60-70% in the winter and often well above 80% during summertime. While I would suspect that lower temperatures are generally a good thing, the quite high humidity might be harmful?

This is absolutely non-scientific and totaly anectodal but I found that a combination of high humidity and high temperature causes noticably fast yellowing even in the absence of sunlight.

I also disagree with xjas. Brittleness is caused by material degradation on a molecular level, due to temperature. Overtime what really is happening is the molecules in the plastic do to degradation become to short or too long.

This has nothing to do with UV light, it is caused by temperature change and age. Brittleness could be caused by to much exposure to heat but not UV, can also be cause by to much exposure to cold, or too much fluxuation between heat and cold overtime.

If anything getting the plastic really hot in the sun might help it.

It is a misconception that the brittleness is dry rot like in rubber, which is caused by Microorganisms and UV light. It's not dry rot and compounded by dryness. Rubber is an elastomer

ABS is a thermoplastic and can be heated to its melting point, cooled, and re-heated again without significant degradation. Rubber on the other hand is an elastomer very different molecular and chemical substance than the old ABS plastic used in vintage computers.

Proof in concept abs welding using a heating iron is a thing, as well as abs plastic welding using acetone. neither one of these things weaken the abs in contrary both return the abs plastic back to its original molecular level.

In contrast if you heated rubber like this it would molecularity change this is why drag racers burn out their tires for more traction before a race. Because the molecular properties of racing slicks perform better at higher temperatures. The heat causes the molecular chains to expand creating more traction.

In the case of rubber it doesn't return back to it's original composition it gets stretched out after time which then UV light and microorganisms will cause dry rot.

appiah4 wrote on 2020-01-09, 12:21:

Baoran wrote on 2020-01-09, 11:54:

I would like to know if there is a way make things less yellow without sun. I would like to make case face plate less yellow and not have to wait until summer to do so.

Yes, you can use hydrogen peroxide mixed with water, submerge the parts and heat them to around 50C or so, if you have a thermostate heater of the required size.

8-bit Guy has a video about this method.

Any chance if using sauna would work keeping air temperature at 50C? I don't have such heater so I was wondering if I could use sauna to help with that.

I've often wondered after its retro brighted why not apply clear coat to prevent future oxidation of the plastic?

I can't recommend sun exposure. I don't question that it works, but UV damages plastic. That's how it works. Try leaving some child's toys out for years. They will of course be bleached, which is the idea, but the surface of the toy will become soft, cracked, and delaminated. In fact, those cracks may be internal (depending on type and thickness). So that is what happens on a small scale when you leave plastics out. And these are not your fresh from China plastics, they are antique pieces, perhaps of unproven formulation, of reduced strength and likely already have extensive sun exposure from their years of use.

Generally I recommend the hydrogen peroxide bath, but depending on the item's characteristics, if you can fully coat an object, higher strength cream (AKA shampoo) gives much faster results as shown by video.

candle_86 wrote on 2020-01-10, 17:29:

I've often wondered after its retro brighted why not apply clear coat to prevent future oxidation of the plastic?

You can, if you don't mind coating your stuff in paint.

hwh wrote on 2020-01-11, 00:46:

I can't recommend sun exposure. I don't question that it works, but UV damages plastic.

]

Most Children's toys are not made of ABS Plastic. The yellowing of the ABS in vintage computers is not really becasue of direct sunlight. It's becasue of the bromine content reacting to UV-A, and florescent lighting and it took 20-30 years to happen. It not really sun faded.

As you can see in the graph children's toys amount to 10% in ABS, and fact is the way ABS is made today is a lot different than back then, these days they mix carbon into the plastic to keep it from degrading. Such as ABS Black Pipe.

plastic is not plastic.

Warlord wrote on 2020-01-11, 05:50:

The yellowing of the ABS in vintage computers is not really becasue of direct sunlight. It's becasue of the bromine content reacting to UV-A, and florescent lighting and it took 20-30 years to happen. It not really sun faded.

I'm not sure that's totally correct. Or, at least, I don't see how it could be given my own anecdotal evidence. E.g., I have some Plextor SCSI CD drives that I used back in my PII/PIII days. Indirect sunlight at best, mostly ambient light from under a desk in a room with an incandescent bulb and a west-facing window with a large fence outside.

Around 2005, still looking normal, I put them in a motherboard box and stored them in a closet for years. Later I moved them to a garage, that box inside another box. (Cool, dry climate, winters 0-20F, summers 45-70F on average. Heated garage set to ~60F.) I took them out a couple years ago -- very yellowed.

So as far as I can tell, plastic yellows for no good reason at all. Lots of hypotheses that seem plausible, but we're in severe need of controlled tests by materials scientists. 😉 And I totally agree with the above sentiment. There's no good definitive source of information on how various bleaching techniques work, what impact they have on the material, and whether the change is permanent. Just random data points.

My 2c: I prefer to use a hydrogen peroxide bath. Low concentration of liquid seems to me to be the safest, since you're not as likely to overdo it, and the application is more consistent than cream. I plan to build a reflective tub with UV LEDs and fill it with liquid hydrogen peroxide. High heat can damage (warp, melt) the plastic, so tread carefully -- test on non-critical pieces if you can. I don't plan to use any heat.

my own experience is that extremes of temperatures and humidity make it much more likely to be yellowed. This in the total absence of sunlight.

Things kept near room temperature withan average amount of sunlight coming in seem to be a better-case scenario.

I've got a few systems and peripherals that have been out of direct sunlight from 15-20 years. or more and they have yellowed. They were fine when I got them.

Glass that is transparent to visible light absorbs nearly all UVB. So even if something is behind glass its not getting direct sunlight.