I received my formal training in printmaking...silkscreen, lithography, photogravure. I did tons of photo silkscreening back in the 80's. I had my negatives enlarged into halftone positives by a local blueprinting firm. I exposed them onto polyblue using an old arc lamp. I did up to 6 colours. Nowadays, halftone screens can be made via photoshop and inkjet printer. I couldn't locate any polyblue, so tried out the liquid emulsion, and screen from a local screen printing supply shop. I've use the speedball screens and they're crap, as far as I'm concerned. The screen material comes lose. Also prefer oil based ink. Speedball water based ink is crap. I've also done heaps of photo litho, on plates and stones, preferring the latter. These days I prefer carbon transfer, and gum printing.