Here are some basic instructions for washing your custom European license plate:

1. Remove your plate and frame from the vehicle
2. Remove the plate from the frame
3. Use regular dish soap and water to wash both, GENTLY.
4. Put everything back together and re-mount it to your vehicle

Things to avoid:

1. Car Washes (more on this below)
2. Harsh Chemicals (409, Clorox, etc)

I’ve had a few customers complain that their plates have been damaged in car washes. Unfortunately, this is nearly unavoidable. Not only do car washes generally use recycled water (that may have sand and grit), but they often have high pressure washes of 1,000 psi! The general strategy of car washes is to post a sign “Not Responsible For Damage To Customer’s Vehicle.”  If they might cause damage to your vehicle–they will almost assuredly cause damage to your plate.

Here’s an article I found that goes into a little more detail: The Pitfalls of Using Touch-Less and Other Automatic Car Washes