Look up “retrobright”, it’s what multiple communities call using dilute hydrogen peroxide to restore yellowed plastics.

Not sure how to restore them but I do know how to prevent it. Keep the sets out of sunlight and don’t have lights pointed directly at them. They will still fade over time but doing those things slows the damage and makes it less severe.

Keep future sets out of the sun for long periods of time.

I don't know how to fix fading, but you can protect your Lego by keeping it away from direct sunlight.

polywatch? It’s restores watch crystals. They do a version for plastic I believe

Easy? No not really. If you're determined you can look into car headlight restoration kits since it's the same principle, a bunch of micro scratches on plastic.

Go down to your local hobby shop (or Amazon) and get a tube (or set) of Tamiya Polishing compound. I think it comes in three varieties "coarse", "Fine" &, "Finish"

Work the polish in with a microfiber cloth until you're happy with the results. Alternately, you can use a rotary tool (Dremel) with a polishing pad, but be careful because these can damage the plastic if you aren't being careful and also the part you're polishing is quite small -- tricky to handle.

Micro mesh pads, used wet, go through the higher grits, then some car polish

I mean, I'm not sure how you value your time but... New ones are 3-5¢ each on Bricklink. There's no way I'm spending an hour buffing old ones back to life when they're that cheap to replace.

Take everything apart and start from scratch. It’s the easiest way to ensure you don’t miss any steps. I’ve had to rebuild the Batman tumbler twice. First time I tried cutting corners and it made it more difficult.

Try pulling out the larger parts of sets that are still together. Then sort the remaining pieces by color. Take apart each set to identify the parts you have, and then find the pieces you are missing from your sorted loose pieces. It is a good idea to make a spreadsheet to keep track of pieces you can't find.. Then if you find pieces later you can mark them as found or you'll have a list of parts to order off of Bricklink.

yes, there is a method with peroxide to remove the yellowing, you can search for it, there are many posts on it, but it also isn't permanent and it can degrade the bricks.

Don’t put chemicals on your Legos. Just buy some replacement parts on pick a brick.

Good luck.. I have one of my hubs old sets from lord knows when that I was thinking about putting together. I haven’t decided how I’m gonna separate them yet though. It’s pirate ships. I also have a bunch of the avengers sets and Disney and Minecraft sets that were my kids. Thinking about doing them as well.

On the bottom of the 5th image there's a red/yellow flame place (solid color) do you remember from what set it is?

Sorting by color makes it so hard to find parts. Sorting by type is the way to go.

Oh my gosh good luck! I am actually kind of jealous, that looks like a blast

That last picture scares me.. not by color but by type.. you’re gonna have a hard time finding that 1 red 3 in all that mess.

Search "peroxide" and you'll find all kinds of posts about this

I thought that color was the real color omg

Dishwasher

Put them in a higher tax bracket

soak discolored Lego pieces in 3% hydrogen peroxide, placed in direct sunlight.

This is why Lego is so bad for the environment. It lasts forever. Even the print is still there.

Can't relate. My collection dates back to the mid 80s to now. Aside from the usually brittle pieces from a specific decade, everything is still clicking together firmly. My collection is currently in a climate controlled room in the house, but it has been stored and played with in a non climate controlled garage that experienced temps from below 0°C to above 43°C for more than a decade.

How long did you have them assembled? Plastic that is under stress will creep over time, leading to permanent deformation. LEGO is made to be assembled and disassembled repeatedly, as long as parts are assembled they are under a certain amount of stress which is unavoidable.

Repeated assembly and disassembly that does not strain the plastic beyond the elastic limit will not harm the parts significantly, but leaving them assembled for extended periods of time may.

I routinely disassemble all sets that I build and order quite a lot of used bricks and my experience has been that by the 7 year mark most bricks lose the slightly oily coating that they come with from the box, which is probably why they become a little less smooth to connect and disconnect.

Not sure how your experience has been, but at least for me the bricks have still been very much usable, the different tactile feeling just takes a little getting used to.

I'm wondering if a call to Lego customer service might shed some light on this?

Curious what ol you find I’ve displayed for 5yrs and am unbuilding so curious what the group says!

Don't try chemistry on yellowed bricks :-( Use them.

I get asked how I achieve that unusal, not Lego like look in my mocs.One point is that I love using old white plates for medieval houses :-)

Here are some examples:

https://www.flickr.com/photos/154489981@N04/49293819128/in/dateposted/

https://www.flickr.com/photos/154489981@N04/29915639638/in/dateposted/

https://www.flickr.com/photos/154489981@N04/28965193308/in/dateposted/

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There are quite a few other factors as well to achieve such an organic run down look:avoiding light reflections when doing pics,using small parts and many tiles (tiles have more structure),techniques that allow discrete placements of the bricks (hoses, hinges etc.)

I use the old grey pieces for the same thing! The new greys look a little too blue for some of the aesthetics I'm going for. Thanks for helping normalize using off color and mismatched bricks lol

Op I just gotta say, I absolutely love these little follow up posts showing the little things you did to get that plague moc perfect!

Holy moly that's a wholly new level of Lego.

Okay now show us a yellowed brick road