Naphtha isn't quite as dangerous as it sounds...Don is right...

But I'd be sure to use it in a well ventilated area...

I think acetone is your best bet...dries fast, you can buy it
cheaply at the store (nail polish remover)...and won't harm the
plastic card...

I don't know this for a fact, but I think you could potentially harm
the slot card if used (naphtha) excessively....but I don't know that
for sure....

Make sure you use chemical resistant gloves when handling naphtha...it's
nasty stuff.

Katie