In fine and resto work Ive come to be a believer in the adage,' use a scraper made of a softer substance than the base you are working on'. For steel I often use brass scrapers, and any brass is softer, but for brass or aluminum there are enough different grades that you can use a soft brass on harder brass, etc. Making the scrapers is easy enough out of scrap stock, but an easy brass one is a 30-06, or similar, empty cartridge case. It is long enough to give you a good grip and the neck can be easily flattened and shaped for what you are doing.
The credit card thing has also worked for me, but the edge rounds off quickly, so keep rotating the card when it stops doing what you want.
BTW, it is always better to start with too soft a scraper than too hard a one! You can always escalate your attack, but scratching the base will cause wailing and gnashing of teeth.