As an alternative to using photographic techniques to make a heater PCB for a Reprap or similar 3D printer the copperclad laminate can be marked for etching with an etch resist pen using the 3D printer itself to do the marking. The plotting in progress can be seen on https://www.youtube.com/watch?v=XfjI_UXrnJ8
The instructions are in a PDF file in the source files. Also there are a text G code file and a spreadsheet file which was used to produce it.
Please ignore the DXF file. It was needed to get round Thingiverse's insistence that GCO files were not manufacturable