While digging through my LEGO pieces to reconstruct my train sets, I would frequently come across some severely discolored pieces. They were from a LEGO R2-D2 set, number 9748 in the Mindstorm line of electronics-enhanced kits. I had my little astromech droid displayed on my office window ledge for several years, causing severe sun damage on some of the plastic pieces. I disassembled the kit and distributed its component parts into my LEGO organization system, intending to use those sun-yellowed pieces as internal structure of future creations where we wouldn't see the discoloration. That never happened, so now I'll rebuild the droid with an extra challenge: I want to reconstruct the droid including its sun-yellowed nature.

You see, the discoloration only happened in places where certain pieces were exposed to sunlight. The original colors were preserved in places shaded from sunlight. Here are some examples of white pieces with discoloration only where sunlight could reach. A piece of standard LEGO white plate and a standard LEGO tan plate are at the bottom of this picture for color comparison.

Even though R2-D2 only had three wheels, this kit came with four wheels in the box to support four-wheeled creations. While three of the wheels were sitting on the window ledge, the fourth was stored away, and we can see a severe difference in the soft rubbery gray parts of the wheels. In contrast, the rigid gray plastic hubs were barely affected by sunlight exposure.

Obviously different plastic formulations had to be used for soft tires versus rigid plastic. But this kit taught me not all rigid LEGO pieces used the same plastic formulation, either. Many pieces in this kit looked white when new but, after receiving a lot of sunlight, some were immune to sun damage and remained white while others yellowed. It appears all the sun damage immune pieces were Technic-style studless construction pieces, but not all studless pieces were immune.

Reconstructing this yellowed R2-D2 meant physically identical LEGO pieces were not interchangeable as they would normally be. I had to investigate adjacent pieces to make sure their shadow would align with sun-yellowed borders of specific pieces.

Thanks to paying attention to sun-yellowed borders, the recreated R2D2 didn't have blotches of white exposed in the middle of bricks that were formerly shaded. It still looks weird with a mixture of sun-yellowed parts attached to parts immune to sunlight damage, but I'm going to call it character.

A day after I reconstructed this, all four flexible beams used to define R2's shoulder curvature broke. I don't think this is sun damage, I think this is age. Formerly soft plastic could no longer sustain such a tight curve and failed. Maybe I can 3D-print some replacements out of TPU or similar flexible filament, but I'll leave them alone for now as part of veteran R2's character. I have other R2 sets to reassemble for a group photo.