
Your brass was not scraped off and the spots are indeed a result of dezincification.


Instruments are made from solid brass, this is required as a stiffer metal like brass is required to have good sound quality. How do I identify dezincifiaction correctly? Can it be seen on those pictures? (most important question)

Now I learned that the brass contains zinc, and there is a corrosion process called "dezincification". I do own a brass instrument (a trombone).
