Toner is a powder used in laser printers and photocopiers to form the printed text and images on the paper. In its early form it was a mix of carbon powder, iron oxide, and sugar. Then, to improve the quality of the printout, the carbon was melt-mixed with a polymer. Toner particles are melted by the heat of the fuser, and bind to the paper.
In earlier machines, this low-cost carbon toner was poured by the user from a bottle into a reservoir in the machine. Current machines feed directly from a sealed laser toner cartridge.
Modern laser toner cartridges intended for use in color copiers and printers come in cyan, magenta, yellow and black (CMYK).
Read more about Toner: Composition, Size and Manufacture, Clean-up, Health Risks, Environmental Considerations