An Experiment on Brick Yellowing by Sunlight

[Vorkosigan]

I was recently inspired to do a simple test on the effect of sunlight on brick yellowing. This May I had new windows installed in my house and this has resulted in more time with the curtains open enjoying the views and sunlight. I started to worry about the effect of sunlight on my MOCs and trays of bricks for builds in progress. The new windows have a coating that is supposed to improve energy efficiency, its called "SmartSun" glass. I also wondered if this would reduce the risk to the bricks. So what I did was place 4 sets of brand new white bricks in various sun exposure conditions. All were on the south side of the house for the last 6 weeks (summer in my area). The white bricks sandwiched by red bricks were taped to the outside of a window directly exposed, the blue were just inside the same window. The yellow set was behind a patio door with glass that is approximately 25 years old. And the black set was left in the dark the whole time.

The results are essentially a lack of results, I saw no yellowing on any of the bricks, see pictures below. Now 6 weeks is not the same as years, and bricks mounted vertically are not the same as a build that is actually outside with the sun beating directly down on them. But for my purposes of concern about LEGO being exposed a few hours a day, indirectly through a window, this 6 weeks of continuous exposure is equivalent to at least several years worth. I'm still going to avoid excessive exposure to sunlight for my builds, but this definitely reduced my concern.

[Mesabi]

Yeah, it must take longer for bricks to yellow. Maybe keep it under for another 6 months, you know For Science!

[davee123]

The trouble is that ABS plastic is really complex in terms of structure, which means that not all batches of plastic will behave the same way. Typically, when I see a model start to yellow, it's because a few bricks here and there start yellowing-- it doesn't happen all at the same time. Some pieces are more resistant to yellowing than others.

It would probably be a good idea to test with a variety of different types of elements, rather than just 2x4 bricks (quite possibly from the same batch). Try a small bunch of them, like a 1x1 brick, 1x2 brick, 1x3 brick, 1x4 brick, and the same sizes in plates, all stacked up in a 1x5 rectangle. That way, it's more likely that each one came from a slightly different batch of plastic, and are more likely to yellow at different rates.

DaveE

[LegoMedGuy]

I would also suggest that you try this with plates. Perhaps how thin the brick is could influence the rate of yellowing. Something about ratio of surface area to volume?