Yellowing in MISB sets

[caperberry]

Yes read that other thread, lots of info there. The one on Brickset Forum has good comments too, including some fairly controlled experiments by a Danish LUG. Search for "unyellowing" and you'll find the thread.

Mark Stafford said something interesting at AFOLCON 2012 in Manchester. If I remember correctly (which I don't always!) he suggested total darkness is not ideal for preventing yellowing and that translucent plastic containers are best.

[L@go]

It's also, from what I've been told by LEGO insiders, dependant on the specific chemical mixture in any particular batch of bricks - some batches are more prone to discoloration than others. I've seen 10-15 year old MOCs built from a number of white bricks, obviously from different sets and probably different time periods, where some bricks look pretty much as white as they were when they first came out of the box, whereas others could not possibly be distinguished from a modern part in tan. And they had all been connected to the same bricks since the MOC was originally built - i.e. stored in the same place and exposed to the exact same conditions.

[Faefrost]

It's also, from what I've been told by LEGO insiders, dependant on the specific chemical mixture in any particular batch of bricks - some batches are more prone to discoloration than others. I've seen 10-15 year old MOCs built from a number of white bricks, obviously from different sets and probably different time periods, where some bricks look pretty much as white as they were when they first came out of the box, whereas others could not possibly be distinguished from a modern part in tan. And they had all been connected to the same bricks since the MOC was originally built - i.e. stored in the same place and exposed to the exact same conditions.

The chances are this is something that Lego probably had limited control over. During that time period weren't they still fully using pre colored pellets from Bayer? I believe the Flame Retardent is added during plastic production, not simply melting for casting. And plastics companies were and are constantly tinkering with the additives. So it isn't so much what batch the bricks came from, as what batch of plastic each in turn came from. And figure there was even more variations as different batches of pellets were mixed. I'm thinking "color shift after 20 years" was probably not a key testing metric at the time.

[Karto]

Another possible reason:

Your set might have been restored. Yellowing can be treated with Hydrogen Peroxide (H2O2), BUT depending on the cause of the yellowing (UV, smoke or BFR), the results may not last very long. I have treated sets that showed equally yellowed bricks. It looks like this is usually caused by the Bromine Flame Retardants breaking down (Bromine is brown). The results were impressive, but after a few months without any UV/Smoke exposure, the yellowing on white bricks came back and got even worse. I cannot recall having the same issue with other colors such as grey or blue...

If the blue bricks were also treated against yellowing, they might look slightly lighter than other blue bricks from the same period.

[CP5670]

Bumping this old thread after many years. I finally got a chance to try out retro-brite (H2O2 in a gel form), available as a commercial product now. Some 80s/90s sets I had on display for 15+ years are quite yellowed now, like 8880, 6483, 6398, 5563 and some others. Only some specific bricks are affected, and as discussed earlier, the yellowing is uniformly spread out over the whole brick. I used a toothbrush to put this stuff on the bricks and put them in a sealed bag outside in the sun. The results look good and just like a new white brick, although it did take 3-4 days to see a clear improvement. I'll have to see how long the improvement lasts and if it reverses or not.

It's a bit tricky to make sure all sides of the bricks are exposed to sunlight, and I had to flip the bag and rearrange the parts inside each day. I might try using one of those UV light boxes for curing plastic instead of this approach.

Edited February 19, 2022 by CP5670

[CP5670]

Update on this after two years, most of the retro-brite treated bricks still look great and like new. However, some specific bricks from early to mid 1990s sets (the "oxygen sensitive" white bricks) have become yellowed again and reverted back to how they were before the treatment. It only happens with these specific bricks and it's very obvious because other bricks from the same sets are fine. I'm redoing the treatment with these parts since there aren't that many of them, will see how long it lasts.

[Alexandrina]

15 hours ago, CP5670 said:

Update on this after two years, most of the retro-brite treated bricks still look great and like new. However, some specific bricks from early to mid 1990s sets (the "oxygen sensitive" white bricks) have become yellowed again and reverted back to how they were before the treatment. It only happens with these specific bricks and it's very obvious because other bricks from the same sets are fine. I'm redoing the treatment with these parts since there aren't that many of them, will see how long it lasts.

Thanks for the update - it's quite useful to know whether the results of a method are actually going to last or not!!

When you say "oxygen sensitive" bricks, are you referring to specific types of part, or just white bricks in general?

[CP5670]

They are specific white bricks in sets from about 1988-2000, treated with some different chemical mixture. They yellow just as fast in a pitch dark room as in the light, while other white bricks on the same models look perfect. The only way to distinguish them is to leave them on a built model for many years. I have such bricks in the 8880 Super Car, several Explorien and Futuron sets.

I'm just redoing the treatment on some of them, but will probably replace them with newer white bricks. But some are rare printed parts that are long out of production.