Homebrew PCBs

hi all
thinking on a simple and cheap method for PCB prototypes.
what will happens if we get an uniform layer of "UV cured paint" over
the pcb cooper, and we will UV cure the paint through a transparency 
were the areas to be etched will be opaque and the desired tracks will
be transparent.
If the cured paint will survive to the next step (etching attack), the
rest is so obvious that I am sure I am missing some fundamentals
somewhere on the process.

pls what am I missing????

thanks in advance

juan