The ins and outs of copiers and toners

My office printer stopped working a few months ago, and I couldn't figure out why.
I changed ink cartridges. I ran cleaning and alignment pages. I reloaded the software. I could occasionally get some text printed, but that was rare.
Finally, I gave up and asked for help - no, I don't ask for directions while lost when driving either, until at utmost need.
The technician - a lady much smarter than me - determined the black ink cartridge was bad. No, the cartridge wasn't empty - I'm not THAT office equipment-illiterate. But it seems that when I replaced an empty cartridge, the new one was faulty.
More adventures with cartridges: Many years ago, working as an instructor for a technical college in South Carolina, I needed to make some copies in our department office. The copier, unfortunately, had run out of toner.
I pulled out the old toner cartridge and made ready to replace it - and promptly dropped the new one.
Fortunately, the new cartridge didn't break. Unfortunately, I did spill toner all over the floor. Toner, in case you haven't experienced it, is the darkest, stickiest substance known to humanity. The mess took me a good hour to clean.
What have I learned? First, "cartridge" is an evil word. Second, I'm letting other people replace them from now on. Third, this gives me a chance to talk about how copiers (and toner) work.
A copier is a relatively simple device - at least in the appearance of its output - but uses several different aspects of modern physics.
Toner isn't ink, but rather a fine power made from, of all things, a special kind of plastic. Colors come from various pigments - black being a blend of several.
Toner particles, which are very small, are stuck to slightly larger particles called "beads" while inside a cartridge. Each bead has a very slight amount of positive electric charge, and the toner particles, with negative charges, are attracted to the beads.
This therefore explains the mess when toner is spilled - individual toner particles are both tiny and sticky.
When making a copy, a bright light flashes and scrolls across the paper you want copied. This light reflects off your original and onto a rotating drum that is both positively charged and is covered by a photoconductive material.
The light kicks electrons off the photoconductive material, which then are pulled toward the positively charged drum. Thus, blank spots from the original are seen as electrically neutral, and don't attract any toner.
Dark regions from the original don't reflect light, and so their corresponding places on the drum remain positively charged. These regions attract the negatively charged toner particles. The copier heats the paper to fuse the toner particles in place, and your copy is literally hot off the press.