How to coach paint a car at home with a 3” brush. Please share

Here I am painting the drivers door of my classic mini,I’m using coach enamel paint,just like the craftsmen did in the 1900s to 1970s it’s a dying art form, I decided to paint my car this way because I was quoted £4000-£8000 for re spray, and this way cost me only £350 yes that’s right £350 inc sundries!
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