Back of CCS cel is covered with black paint

I just got a CCS cel purchased from Mandarake. So far, this is the most expensive cel I ever bought but the condition is also the worst...

Not only the cel was originally stuck with sketch, previous owner probably pulled them apart, so the sketch is torn badly. There are HOLES.

Anyway, my question is that the back of the cel is covered with black paint, and I don't know what this is for, so can somebody help me with this?

Also this was my first purchase from Mandarake (not auction), and is there a way for me to know the condition of cel beforehand?

Thanks!

Painting the back of a cel with black paint is unfortunately a common production technique for when the image will be photographed on a light table with a bright light behind it. Otherwise, the backlighting would shine through the pinholes usually left in and around the normally painted sections. And, yes, it unfortunately sticks to sketches very tightly.

If you can trace the cel to its original place, you probably will see the backlighting effect.

I believe Mandarake does respond to queries in English. To avoid this problem, you might send them a note on their website about the condition of the cel and sketch. But, alas, "skinned" sketches are pretty common for this series.

Thank you for your answer. It shocked me when I got it..