"The Box" is a small but thick cardboard box about the size of a hardcover book, and is covered in painting and drawings.
Most of the freehand pen and ink stuff you'll see on this site is from The Box and was done on blank memo pads, the small type usually kept by the phone for messages. A lot of these drawings were done with the intention of simply filling up the box and having it be some kind of "special collection"- that stuff all sounds so cool when you're a kid. I could imagine "them" making reproductions of it, inside and out. "Have your own copy of 'The Box Collection'". )
As for this image, it's the top of the box- which, perversely and true to form for me back then, is actually the bottom of the box (the smaller half that fits inside). The cardboard is wrapped in colored paper that gradualy fades from yellow through orange and red; I painted and drew over it. The image is signed on both sides so that it can be either the top or bottom of a mushroom cloud. (It's currently shown here as the bottom- which is the way I painted it. But notice that there are stars and black space beneath the ground and blast. I was very into taking accepted rules and viewer expectations and reversing or negating them somehow.)