Brass Instrument: Dezincification or just scrubbed off?
Brass Instrument: Dezincification or just scrubbed off?
  
  
    How do I identify dezincifiaction correctly? Can it be seen on those pictures? (most important question)
  


Instruments are made from solid brass, this is required as a stiffer metal like brass is required to have good sound quality. Your brass was not scraped off and the spots are indeed a result of dezincification. Water could get here for a number of reasons from fog mist to moist hands, it does not have to be saliva only. 


  What do you think of chemical cleaning? It sounds dangerous to me. Isn’t it going to damage the instrument?


From what I can find chemical cleaning looks like they use a mild acid and chelatior (like citric acid or EDTA) to etch away some of the red rot. However the brass still has to be polished and the lacquer needs to be reapplied.


  What do you think of cleaning such an instrument soap? Is this going to damage the lacquer or material?


Soap won't damage the lacquer, but scrubbing might. That said your red rot shows that the lacquer is already damaged to you might as well scrub/polish the spots and reapply lacquer.