The versatility of the screen print is that the medium can be so much more than a typical "key block" + color plate 01 + color plate 02 + color plate 03 = a perfect edition. When printing any portion of a print, wether it be a "key" drawing, a color flat, or anything, a dialogue occurs between the artist and the image, with the screen as moderator. What this means is that screen printing is a re-active process and no two images in an edition need to be identical. This reactivity is due to using water based inks.
Today screen printing in the US is done with water based inks ( when I was printing in Slovakia, the shop still used oil based inks for screen print ). There are two advantages of using water based inks when printing an image through a screen: they wash out of the screen fast, allowing you to switch out colors in the same screen; and they can dry as quick as 15 seconds.
These two advantages are used in conjunction with one another to create a re-active process during printing. Because the ink can be washed out of the screen quickly and the inks dry quicker than the time it takes to print an edition of 12, a new color can be switched into the same screen and the whole edition ( or half ) can be printed a second time. Or a third time.. or fourth…
The dialogue between the artist and the image I am referring to is built on the process of reacting to what happens when a color is printed onto the image through the screen. Because of the quick, reactive nature of using water based inks, a print can completely change looks in the time it takes the edition to dry; and the minute or so it takes a new color to be switched into the screen. That is the advantage to using water based inks.