Homebrew PCBs

hell members
I often see,that there are qualified chemist people here in the group.
 
So I have a question about the peroxide types etchants.
Its often told that they only last  4 weeks,if they have been dissolved in water..
How does it look when the peroxide is in the solid form ? does it have a limited liftime ?

So does it take much of liftime ,if it is stored and it is not dry.
and how long does a solution with water actually last ,to be usefull.
thank you for any response 
alex
denmark