This is the way to really get control of the medium, right down to affecting the structure of the emulsion itself. There are few places in the world that offer such facilities (unless you invest in all the darkroom kit, chemicals and specialised tanks). Fortunately there is an excellent lab in Holland called the FILMWERKPLAATS which is very well equipped and runs excellent hands-on training courses and offers very competitive and professional advice. Blow ups to 16mm are possible too. You can get hold of them here: Filmwerkplaats