Homebrew PCBs

I do RF PCBs requiring micro strips etc. It must use double sided FR4 
boards with consistent permittivity and very accurate trace thicknesses 
for impedance matching or inductance chokes.
The hackaday technique assures such results repeatably.
All acids must be handled properly, I have 30 years experience with 
conc. NITRIC and never a problem. HCL is also dangerous, fumes,  and can 
emit large volumes of chlorine if it comes into contact with household 
ammonia cleaners.
http://www.flinnsci.com/media/396140/acidsafety.pdf

When nitric is etching copper it bubbles a bit and self stirs the mix 
for cleaner trace edges I have found. Also the fine even bubble 
generation reveals any improperly cleaned copper areas within a couple 
seconds. Such areas can lead to longer immersion times which will cause 
over etching of the properly cleaned areas. In effect it gives me 
quality control feedback that other etchants don't.

Further, the copper nitrate end product is beneficial to sewer systems 
for restricting root growth, a fungicide or as a soak for preserving 
outdoor wooden surfaces.

  * Cupric Nitrate (Copper Nitrate) Cu(NO_3 )_2 �nH_2 O, green powder or
    blue crystals which is soluble in water; used in electroplating
    copper on iron; as a catalyst and nitrating agent in organic
    reactions; component in rocket fuel; fungicides and wood
    preservatives; textile dyeing and printing; pigment in ceramics;