Homebrew PCBs

Hi Group

With increasing experience, I often end up with printed transparencies 
of a design where the PCB is made, but I want to keep the transparency 
so as I can produce new PCBs of that design if the need arises.

Silly question, but how do you guys store those? I print them wiht an 
ink jet printer (Epson Stylus C62) and the transparencies are dried etc. 
However, I'm afraid that the ink may reacts and taps to the transparency 
below it etc. if I just stack them in a box or so...

How do you guys store such transparencies?

TIA

Markus