Cleaning LEGO and dealing with yellowed bricks safely

TUREFF• •0

Bricks bought second-hand, rescued from a loft or simply played with for years end up dusty, sticky or grimy. They clean up well with care, but heat and harsh chemicals can damage them for good. LEGO (a trademark of the LEGO Group) publishes its own cleaning advice, and this guide follows it, then turns to the trickier problem of yellowing.

What LEGO itself recommends

The LEGO Group's customer service pages advise:

Wash by hand in water no hotter than 40°C (104°F), using a soft cloth or sponge.
Mild detergent is optional; rinse the bricks in clean water afterwards.
Do not use a washing machine, dishwasher, oven, microwave or hair dryer.
Let bricks air-dry at room temperature, and do not dry them in direct sunlight.
Do not soak pieces with electronics, metal parts or stickers. Wipe them with a damp cloth instead.

Hot water and heat can warp bricks so they no longer fit together properly. That is why the advice is so firm about dishwashers and ovens.

A practical washing routine

Sort out anything that should not get wet: lights, motors, battery boxes, cables, pieces with metal parts, and stickered or printed pieces you care about.
Separate stuck pieces with a brick separator. Water will not reach dirt trapped between joined bricks.
Use a large bowl or a clean sink of warm water with a small amount of mild washing-up liquid.
Soak for a while, then work over the pieces by hand. A soft toothbrush helps with tubes and corners. Avoid scouring pads, which scratch.
Rinse in clean water to remove any soap film.
Dry thoroughly by spreading the pieces on towels in a single layer and turning them now and then. Hollow pieces trap water, so shake them out and allow a day or two.

A mesh laundry bag holds small pieces together while rinsing and stops them disappearing down the plughole.

Stickers and prints

Stickers can lift and peel if soaked, and printed parts can wear if scrubbed. Wipe them gently with a damp cloth, keep them out of the soak, and dry them straight away.

Disinfecting

If you want to disinfect bricks, for example from a charity shop or after illness, washing with warm soapy water as above is usually enough for home use. Avoid strong solvents, which can damage the plastic. If you use any other product, check that it is safe for plastics and follow its instructions carefully.

Why bricks yellow

White, light grey and some blue bricks from older sets are known to turn yellowish over time. Exposure to light, especially sunlight and UV, and to heat speeds it up, which is why one side of a model on a windowsill can discolour more than the other. The exact chemistry is debated, and it is not simply a surface stain, so ordinary washing does not remove it.

Can yellowing be reversed?

Some collectors use a method borrowed from the retro gaming world, often called retrobrighting, which uses hydrogen peroxide and strong light or UV to bleach plastic back towards its original colour. Think carefully before you try it.

It is not an official method. The LEGO Group does not recommend it.
There are many reports of treated plastic becoming more brittle, and of the yellowing coming back over the following years. Long-term evidence is limited and mostly anecdotal.
Results are uneven. Bricks can come out blotchy, and prints and stickers may be damaged.
Hydrogen peroxide is hazardous, particularly at the higher strengths sold for hair or cleaning. It can burn skin and eyes. Wear gloves and eye protection, keep it away from children, and read the product's safety data sheet and label.

For many people the safer choice is to accept a little yellowing, use those bricks inside models where they are hidden, or replace key visible pieces with new ones in the same colour.

Preventing it in future

Display models away from direct sunlight and heat sources, use cases or cupboards for valuable sets, and store loose bricks in closed, opaque containers. Have you rescued a dirty or yellowed collection? Share your experience or questions in the comments.