>>6037954>are there are ways to brighten up old white bricks?Toothpaste will work for removing dirt that's actually on the surface, but if you want to whiten old, yellowed bricks, your best option is to submerge the pieces in hydrogen peroxide in a transparent container that's left in bright sunlight for a few hours. Stir the parts well every few minutes, because bubble will constantly form and those will affect the uniformity of the whiteness.
The reason white plastic yellows with age is because the bromine that's added to the plastic to make it flame-retardant starts to turn brown as it breaks down over time. I've had fantastic luck with this technique, even with pieces that are 30+ years old.
Just google "lego white hydrogen peroxide" and you'll find a lot of sites talking about different techniques using hydrogen peroxide.
