They still dip them in a big bath
The actual chemicals they use I don,t know because that's their trade secret
From what I remember many years ago it got dipped in caustic taken out washed and that was that
This method is the car is dipped in a solution which stops all rust as in back to bare metal
Then the car or panels are dipped to remove all paint dirt grime etc
Then pressure washed and redipped and so on till all clean
Then redipped back in the first bath which neutralises the cleaning solution and this is what
leaves a phosphate coating on the bare metal so surface rust won,t set in unless you get the panels wet or
you are near salty air but once you start working on them you have to prime
And as people are saying the solution gets into all the hidden places and so does the neutraliser
Anyway you are left with a perfectly clean surface to work with and no hidden suprises
When I dropped mine off I looked at Mid Life Crisis hatchback before and after it was done and its amazing what it showed up
that had been covered up
Anyway its up to each person to do what they want im just sharing my experience and hope it sheds some light on the subject
Cheers Peter