Homebrew PCBs

Hi all,

I'm thinking of making a DIY spray etcher, using sodium persulphate, 
but wondered if you experts could answer some questions for me ;-)

In a professional spray etcher, are the boards horizontal? If so, is 
the etchant sprayed from above or below? I'm worried that a 
vertically hung board will result in uneven etching due to the 
etchant running downwards, and a horizontal board sprayed from above 
will quickly become covered in used etchant, reducing the 
effectiveness of the fresh etchant arriving... Is spraying from 
underneath possible/workable?

Does anyone have experience of professional spray etchers that they 
could share with the group?

TIA

Duncan