[TheForge] Copper Patina Methods

[Robert J Hill]

Hello,
I am trying to patina copper sheet for a door project.  I'm using  
Birchwood Casey M-38,
https://www.birchwoodcasey.com/store/antiquing.html
I am applying the chemical cold onto a sandblasted, 220 grit sanded  
and scotch brite rubbed surface.  The smaller panels took some work  
but they have a nice deep leathery brown color.  The bigger panels  
aren't blending or taking the color evenly.  They were cleaned with  
denatured alcohol before applying the chemical.
I am wondering what methods and techniques other people use?  Are  
there any good web pages or books on the subject?
Thanks,
Rob