When drum, with it's latent image, rotates to toner area, it attracts toner to drum only where latent electrical image is. In other words toner is attracted to electricity that's left on drum in form of latent image I just discussed. At this point there is a visible image on drum made up of toner. When drum rotates further toner is transferred to paper that is now passing through printer. The toner is pulled off drum by another corona strip or wire that has a higher voltage than drum thus releasing toner onto paper. This corona is below paper so paper is passing between corona and drum. If you removed paper from printer at this point you would be able to see image on paper, but don't sneeze because you could blow image right off paper. After image is transferred to paper it must then pass through fixing or fuser rollers where a combination of heat and pressure permanently bonds toner onto paper.

Sometimes toner gets on coronas which can cause black or white streaks. Some laser cartridges come equipped with corona cleaners. Other parts that can go bad are cleaning blade that cleans drum or drum itself can wear out. Replacing these parts goes way beyond this article.

Mostly, laser cartridges just run out of toner and other parts are fine. The prices of some laser cartridges can go well over $100.00 so a few refills can really save you a bundle of money.

Now keep in mind that they do not buy just any cartridge. They are mostly interested in those cartridges that contain print heads, like HP, Lexmark, Dell, Some Canon, Apple, Some Brother, Sharp and older Xerox cartridges.

The reason is because cartridges that are just ink tanks, i.e. print head is permanently mounted in printer, are cheap for generic market to reproduce. So there is no profit in commercially refilling them.

Also, in order to keep highest quality, they are mostly interested in virgin cartridges, those that have never been refilled. You may find some companies buying once refilled cartridges but at a substantially lower price. Many will just tell you up front that they must be virgin cartridges.

These empty cartridge buyers are easy to find. Just do a Google search something like this, "we buy empty inkjet cartridges". I got over 95,000 results with that search.

This company will supply everything you need for fundraisers. http://www.inkbank.com

Here are some others that will buy your cartridges:

http://www.cartridgesareus.com http://www.webuyempties.com http://www.tonerbuyer.com http://www.fundraisingweb.org/listings/recycles.htm