How do you keep (newer) white bricks from yellowing?

[CSEverett1759]

Supposedly white bricks yellowing is only a problem with bricks made before they switched to a new plastic in the mid-2000's. But having just built a massive Saturn-V mod MOC, I took the Saturn V built directly from the parts that came in the set, bought from Lego, and now the entire thing's horribly yellowed. Meanwhile recently only some specific bricks from Lego's modular buildings diner went fully yellowed in what seems to only have been a year or two. While the diner was on display on the main floor of the house, the rocket has been sitting in a dark closet for at least the last six years! (Hasn't been opened in long enough that it smelled when I did open the door.) It's possible the Saturn V had yellowed before that point though.

Which brings up the question - with "last several years" bricks, is there any way to stop them from yellowing, or do you just need to completely remove them from any possible sunlight (or not display them in a room with any windows), or is there a way to safely display them in a house full of windows on the west side?

Thanks.

[icm]

Dunno where you heard that yellowing is only a problem for bricks made before the mid-aughts. I never heard that 

[Mylenium]

All plastics age and will change colors, even modern ones. There is no magic way of avoiding that. It just shows up on bright colors as apparently they reflect all colors of the spectrum. Darker colors simply absorb them and thus the effect is often barely noticeable. Everything else is a myth based on false information. LEGO are going to introduce a more opaque, more stable white pigment this year, but even that won't change basic physical and chemical laws. And officially they never made any statements that would support your hearsay, anyway. Pigmented pellets typically only make up below five percent of the whole mix, anyway, and in turn that means that there is a whole lot of milky-ish transparent base polymer that will still do its thing and eventually turn into those shades of yellow and brown that combined with white will blend into those off-white shades. Yes, of course it helps to keep your models away from aggressive light with a high amount of UV just as it helps to control air humidity and temperature, but ultimately there just is no way to keep plastics perfect for forever.

Mylenium

[CSEverett1759]

8 hours ago, Mylenium said:

All plastics age and will change colors, even modern ones. There is no magic way of avoiding that. It just shows up on bright colors as apparently they reflect all colors of the spectrum. Darker colors simply absorb them and thus the effect is often barely noticeable. Everything else is a myth based on false information. LEGO are going to introduce a more opaque, more stable white pigment this year, but even that won't change basic physical and chemical laws. And officially they never made any statements that would support your hearsay, anyway. Pigmented pellets typically only make up below five percent of the whole mix, anyway, and in turn that means that there is a whole lot of milky-ish transparent base polymer that will still do its thing and eventually turn into those shades of yellow and brown that combined with white will blend into those off-white shades. Yes, of course it helps to keep your models away from aggressive light with a high amount of UV just as it helps to control air humidity and temperature, but ultimately there just is no way to keep plastics perfect for forever.

Mylenium

How much UV (indoor) can you get away with? One north-facing window that the blinds are always closed on, but somewhat direct line of sight? (New windows that supposedly block 85 percent of UV.)

[Toastie]

5 hours ago, CSEverett1759 said:

How much UV (indoor) can you get away with

You cannot get away with it. It is not solely the UV, it is everything capable of triggering (slow, very slow) chain reactions on the surface/inside the polymer. Depending on the actual formulation, sometimes yellowing occurs faster, sometimes later. And 2 ... 5 ... 10 ... 30 ... years is nothing for a slow chemical reaction. It is called half-lives in physics and chemistry. 

UV certainly accelerates yellowing. Without UV, it will happen as well. 

Best
Thorsten

[SpacePolice89]

21 hours ago, Mylenium said:

LEGO are going to introduce a more opaque, more stable white pigment this year,

Interesting! Do you have any links or additional information?

[Mylenium]

1 hour ago, SpacePolice89 said:

Interesting! Do you have any links or additional information?

Here you go:

https://www.newelementary.com/2025/05/colours-427-cool-yellow-426-white.html

Mylenium

14 hours ago, CSEverett1759 said:

How much UV (indoor) can you get away with?

The less, the better. Of course none of us live in a dark bunker filled with non-reactive gas and cooled to chilling temperatures. A north-facing window with blinds down sounds as good as it gets. My situation is similar, with additional sun coverage provided by folders and boxes on my long shelf. Either way, no need to overthink this. As @Toastie said it's gonna happen one way or the other. You can only try to slow down the process.

Mylenium

[SpacePolice89]

7 hours ago, Mylenium said:

Here you go:

https://www.newelementary.com/2025/05/colours-427-cool-yellow-426-white.html

Mylenium

Thanks!

[MAB]

On 8/8/2025 at 10:01 PM, Toastie said:

You cannot get away with it.

 

While inevitable, there is the issue of timescales and human lifetimes. Prolonging damage can be good enough, even though it is inevitable in the long term.

On 8/9/2025 at 6:59 AM, Mylenium said:

A north-facing window with blinds down sounds as good as it gets.

And walls painted black to stop any reflections. And maybe UV filter film on the windows for any light that does get in.Temperature controlled too, as cool but stable as possible.

[Toastie]

2 hours ago, MAB said:

And maybe UV filter film on the windows for any light that does get in

No necessary, normal glass does block UV light completely - that's why you don't get a sun burn behind a window, but slowly simmer. If any filters, I suggest blue, red, and yellow filters on top of each other .

Once all light is blocked, use yellow lighting only, as the semicon industry does in their lithography cleanrooms for the same reason.

2 hours ago, MAB said:

there is the issue of timescales and human lifetimes. Prolonging damage can be good enough

That is true, however the process depends so much on the individually used monomer formulation and pigment choice and quality - which should always be the same everywhere but certainly are not and cannot be, should you want any reasonably priced ABS polymer. Some white ABS pieces yellow in the dark, most don't, some at elevated speeds after brief exposure to sunlight, some don't, some actually reach "a lifetime" without yellowing if not exposed to sunlight and so on and so forth.

But yes, there are favorable, degradation process slowing conditions - as discussed: No light, as low as possible temperature, low humidity. Hmm - which results in very low playability.

Best
Thorsten  

[MAB]

5 hours ago, Toastie said:

But yes, there are favorable, degradation process slowing conditions - as discussed: No light, as low as possible temperature, low humidity. Hmm - which results in very low playability.

If parts are played with a lot, at least they tend to yellow fairly evenly on the sides as they get built and rebuilt into different things. Whereas the sets built once and left on a windowsill are going to yellow unevenly. 

I wonder if humidity is a problem for the bricks (as opposed to paper and cloth). In my last house we had a pond and when I cleaned it out we found what I assume was meant to be a boat. From the pieces, I reckon it was made in the 80s. The pieces were scratched but the colours were great. So maybe storing them in underwater mud is the way to preserve them! There is a lack of oxygen and it is reasonably dark.

[Toastie]

51 minutes ago, MAB said:

So maybe storing them in underwater mud is the way to preserve them! There is a lack of oxygen and it is reasonably dark.

Ha! Brilliant - didn't think of that one. It seems that bog bodies are a strongly supporting this approach!

Best
Thorsten 

[CSEverett1759]

Wait - if Lego didn’t change their white brick plastic to prevent yellowing in the mid-2000’s - does that mean that with early 2000’s/late 90’s white bricks (AKA those round technic ones before they put the ugly slot in them) there’s no need to give them extra UV protection? A massive quality of the pre-slot ones in white was the entire reason the launch tower was in the closet to begin with.

[DonQuixote]

At the end, everything will decay, even the universe itself and its particles. That's the way of things. 

[Toastie]

11 hours ago, DonQuixote said:

That's the way of things

True. As in one day, we all have to die. But: On all the other days, we live ... as Snoopy said.

Well, your timescale is a bit - uhm - stretched; it appears as if we have a couple of billions of years before things get really interesting. I guess the current scope is more like "years of protective storage in a closet" 

14 hours ago, CSEverett1759 said:

there’s no need to give them extra UV protection

I believe the "extra" is not necessary - avoid direct sunlight even through window glass and exposure to excessive temperatures. Anything else depends more or less on ... luck.

Best
Thorsten  

[Stereo]

Personally I find the yellowing has interesting stories about the origins of the part.  I have a pirate where one leg is still white, the other's a bit yellow, and the hips are very yellow.  Uniformly across each subpart, 3 different shades.  And then other bricks where you can see the shadow of what they were built next to, and the back is still white.

[TrexT]

On 8/11/2025 at 11:59 AM, Toastie said:

No necessary, normal glass does block UV light completely

That is simply not true.

[Toastie]

2 hours ago, TrexT said:

That is simply not true.

True. My post needs to be more specific and I stand correct:

The absorption of window glass strongly depends on the type of glass used for fabricating the window, number of panes, thickness of panes, glass coating of the window surface, age of the glass and coating, among other many things. The other thing is "define UV". One way of categorizing UV is A/B/C. In my lab, we treat "UV" as light with shorter wavelengths than visible light and not passing borosilicate glass (e.g., "Pyrex"). And this is where I got it wrong: Pyrex begins to absorb below 400 nm and is almost fully opaque below 300 nm. 380 - 315 nm is considered as UV-A though. The same holds true to some extent for some window glass material; UV-A does penetrate to some extent through such material, and thus may induce some bond cleavage in polymers such as ABS.

Sorry for that wrong statement and thank you very much for pointing it out, @TrexT!

Best regards
Thorsten

 

 

[patmat2350]

Tangential discussion:
I used to restore Wen-Mac Texaco Tankers from ~1961. I purchased sad old toys and fixed them up with new self-made parts, sometimes nearly as good as new.

The tankers had two white "houses" made from polystyrene, and I found a huge range of conditions on these parts. Some were hopelessly yellowed, some yellow on one side (I assumed they sat for years on a shelf exposed to a window), and some so white that they must have been kept in the original carton for 6 decades. But that whiteness ruled out simple oxygen exposure, it had to be the light. 

What to do? The yellow was not deep, and some parts benefitted from light sanding and polishing. I also tried a popular remedy: Coating parts with hydrogen peroxide and exposing to MORE UV. Seemed to have some effect, but not enough to fix my parts. Usually the only solution was white paint. 

And it affected the light gray parts as well. When I got started, I matched a gray paint to found parts- it was a gray with a tinge of green, which I used to paint 3d printed replacement parts. Later I found that the gray was UV affected too! Unexposed parts are a "pure" gray with no green tint. Had to get a new paint...

A badly yellowed example:

 

A nice example, un-yellowed after 60 years:

A restored tanker:

Edited August 21 by patmat2350

[MAB]

Painting doesn't really work for LEGO as tight fitting parts rub against each other when assembled/disassembled and you tend to look very closely at LEGO due to the scale.

Edited August 21 by MAB