Lithographs
Colour printing on a large scale was first made possible by the development of a technique called chromolithography. This technique worked by having an image on stones (usually limestone), the stones would have been especially prepared so that some areas would hold ink others would repel it. Each stone would have one colour of ink put on it, multiple stones would then be used to build up a colour image. The more complex the lithograph the more stones are required to print the image, thus creating a higher quality picture. Cheaper lithographs tended to use a minimum of around five to six stones.
The technique became popular though was also controversial. It allowed the reproduction of oil paintings and opened up owning art to the aspirational middle classes. However it was also criticised as being a cheap copy that lacked the soul of original pieces. Furthermore its popularity would be its downfall, as it did indeed become associated with cheap printing and low-quality images.