What causes yellowing?

[Algernon]

Hi,

I've heard reports of white LEGO parts "yellowing" as they age. I'd like to keep this from happening to my newly acquired Ice Planet 2002 collection, and I'd like to know what causes it and if there's any way to stop/slow the process.

Thanks,

Alg

[Buttons]

I am of the opinion that it is only older white bricks and by older I meanlate 60's and older that tend to yellow. I think that newer bricks such as your ice plannet collection are made from a different material that does not yellow.

Please though if I am wrong correct me.

[metalandi]

I always thought this causes from all the light over the years, but i could be wrong. anyway, for example red bricks getting lighter, is definitely a product of light.

[meschepers]

It isn't just the bricks from 60s and earlier that yellow. I have some old grey and white parts that are from the late 80s and early 90s that are yellowed. I do not know what causes them to yellow as my brother and I always kept them stored out of light and no one in our household ever smoked. I think that it is most likely just something that comes with age and use. I am sure that there is a way to clean them once they have yellowed but I am not sure how one would go about it.

[Buttons]

I am sure a chemist would know of a chemical to try

[Natman8000]

Perhaps from the chemicals slowly oxidizing over the years? Keep e'm in your freezer is my best solution!

[CP5670]

Yes, this is basically the result of oxidation, which is accelerated a lot by UV exposure. The best way to avoid it is to keep your Lego in a somewhat dimly lit room, without direct exposure to sunlight. It's a good idea to cover up any windows in the room, and possibly also to use incandescent lighting. If you can block the sun, that should mostly fix the issue. I have had white models on display for several years without any problems. This mainly affects white bricks, but can also be seen in gray and blue to a lesser extent.

Now there are also a few rare pieces that oxidize due to a different cause and will actually get discolored faster in a dark room. I have a few select pieces from some early 90s sets that are like this (some of which are quite rare too ). TLG has confirmed the existence of such bricks too, but I haven't seen this phenomenon in anything from the last several years.

The yellowing process can be reversed, although it's not really simple to do. Someone here (Bonaparte I think) managed to do it pretty effectively using some kind of industrial grade bleach and giving it a lot of time.

This article has some interesting information on this issue.

Edited January 18, 2009 by CP5670

[mania3]

I bought a box of used LEGO pieces and some of the pieces were so horrendously yellowed it was unbelievable. And the unfortunate thing is that most of the sets were from the late 90s. My assumption is that this was due to sun exposure. I think the proof of this would be in the fact that there would be pieces that were connected and on all of the exposed areas the yellowing occurred but when you separated the bricks the portions that were covered looked pristine. But I can say that brown, gray, red, blue, and white were all significantly affected by the yellowing.

[SWMAN]

I think that age, sunlight, and smoke would/will contribute.

[CP5670]

I bought a box of used LEGO pieces and some of the pieces were so horrendously yellowed it was unbelievable. And the unfortunate thing is that most of the sets were from the late 90s. My assumption is that this was due to sun exposure. I think the proof of this would be in the fact that there would be pieces that were connected and on all of the exposed areas the yellowing occurred but when you separated the bricks the portions that were covered looked pristine. But I can say that brown, gray, red, blue, and white were all significantly affected by the yellowing.

Yeah, if only some sides of the bricks are yellow, it's definitely the UV form of it. The other kind I mentioned occurs uniformly across the entire brick, including any covered parts.

[Brickvergnugen]

I've seen this yellowing in some white pieces I have from the late 70's and early 80's. Interestingly, they are incredibly well suited for creating buildings that call for a weathered look (i.e. Spanish missions like this one: http://www.brickshelf.com/gallery/jeffe/pi...3-3339_img.jpg)

Those discolored bricks add a texture to the coloring that new bricks cannot offer.

[Monki]

This article has some interesting information on this issue.

I think you've placed the wrong link by mistake, The link provided is for a 'vintage computing' site

[CP5670]

I think you've placed the wrong link by mistake, The link provided is for a 'vintage computing' site

I left off the last digit. This is the link. It's about old SNES and Mac casings, but they are made of ABS and a lot of it is relevant to Lego as well.

[paksu]

I am sure a chemist would know of a chemical to try

There are reports right here on EB on attempts to reverse yellowing using bleach, industrial grade bleach, and Hydrogen Peroxide.

Edited January 18, 2009 by paksu

[Algernon]

How do you tell if a brick will yellow faster or slower in the dark? XD

[Fluyt]

They mainly get yellowed because of (sun)light and also smoking. Most colours get yellowed I think, only it is most noticable in white, light grey and transparent colours, but if you look closely at darkgray, red etc. you see a difference between new bricks and bricks that have been around a while.

I don't think the age of the bricks has much to do with it (only older bricks are more likely to be yellowed, since they've been around longer and have been more likely to have been left out in the sun).

The only (good) cure to get them in better shape is to use bleach or something similar, as was already mentioned, but as far as I know, if not done correctly it can also hurt your bricks+ it is not guaranteed to work.

[CP5670]

How do you tell if a brick will yellow faster or slower in the dark? XD

If in doubt, it's the latter. The only bricks I have that behave the other way are from a few old Technic sets, and only some specific pieces in those. Some examples are the 1x8 plates in the 8839 Supply Ship (only those plates, nothing else), the wheel hubs and transmission cover plate in the 8880 Super Car, and the (non-ABS) white axle joiners in the 8480 Space Shuttle.

Edited January 18, 2009 by CP5670

[Karto]

As said before, there are two main causes for yellowing:

• Sunlight

• Smoke

I have parts from 1958 which are in perfect condition (in Cellulose Acetate, even more fragile than current ABS bricks). Bricks won't yellow just by aging. ABS is a strong base material and if stored correctly, it won't move in a century. If you keep your bricks from sunlight and from smoke, you're safe. They'll age only by the way you handle them (scratches, etc.). In my case, I kept a Black Sea's Barracuda for 15 years, uncovered in a dusty, dry and cold place (ceiling) and after cleaning, parts were as new.

If you have yellowed parts, you can 'clean' them with Hydrogen Peroxide (H2O2 or Bleach). If you know a good pharmacist, ask for industrial 100 Volume Hydrogen Peroxide (30% concentration if I remember right) but be careful as this is a very unstable and quite dangerous liquid. To be handled with gloves and avoid any conact with skin, cloths and other liquids. Leave the yellowed parts for 24 to 72 hours in the bleach and the thin film of molecules on the surface that caused the yellowing will be removed. If the part was unused, it will be shiny as new. Don't leave the parts for too long otherwise the bleach will attack the shape of the brick itself. It works for all colors, also for grey and blue. Printed parts can also be cleaned this way, the printing won't be affected as long as you don't leave the parts for too long.

[prateek]

OXIDIZATION AND/OR LIGHT!!!!!! put it in an airtight container and keep it away from strong light

[Algernon]

If in doubt, it's the latter. The only bricks I have that behave the other way are from a few old Technic sets, and only some specific pieces in those. Some examples are the 1x8 plates in the 8839 Supply Ship (only those plates, nothing else), the wheel hubs and transmission cover plate in the 8880 Super Car, and the (non-ABS) white axle joiners in the 8480 Space Shuttle.

Ok, thanks. Why do some white bricks yellow when others don't?

[CP5670]

Ok, thanks. Why do some white bricks yellow when others don't?

I have no idea. That article I posted earlier says that companies put in extra additives into the ABS to increase its UV resistance, so maybe they were experimenting with something different back then on a few select parts. The affected pieces otherwise look no different from any other parts.

The only recent reference I've seen to this was a TLG engineer's presentation at the last Brickfair. He brought up this dark room yellowing effect and said "I didn't believe this was possible until they showed it to me," but he didn't give any explanation on why it happens.