go to the search box at the top of the page and write in ecore, then hit search. Lots written here and plenty of pictures with the technique.
Here are a few NanoFry baits I Ecored using a twin injector for the primary colors and followed with black. These are only 1" long.

Somewhere I have a picture of some 1" Ice Ticklers that I did using clear plastic and cored them with glow in the dark colors to get the glow core and tails.