W126 asked a great question and pointed us to a careful warning.

The semi good news is that chemicals that raise the pH to such a high degree (called bases) applied to most metals quickly remove oxides and organics. Bases love organics like, oh, leather or cloth and wet organic tissue like skin and eyes. The potentially disastrous bad news is that unless you scrupulously clean every molecule of a caustic from the surface, the base will pursue positive ions wherever it can find them. If it finds free ions it will form a salt. It will pursue metallic ions from molecular metals if it can't find a handy oxygen molecule. It will discolor or tarnish or etch or erode most kinds of metals.

A safe (for you and the car) way to neutralize a strong base is with a lot of water. Don't use any acid, you already know what happens when acidic material comes in contact with metal.

Wash with soap. Wash the area to which you applied the base then wash everywhere that water splashed when you rinse it off. Then rinse everything again.

I think its an interesting experiment you've performed. The test will be how well you removed the material. It will probably take several months to be sure your cleaned sufficiently. Please let us all know how it looks in September.

---chris