the photo method is much better, I made my own UV unit from 225 UV leds and an old flatbed scanner (yes took about 8 hrs to solder the leds to the stripboard). The exsposure time is 30-45 seconds ! and I develop in a weak solution of caustic soda in about 10 seconds, I've been trying to use the muriatic acid method myself but ended up buying some etching chemical from maplins as it was getting too involved