Foiling was one of the favourite techniques when it came to custom printing. Nowadays we have metallic printing, both techniques will give a beautiful finish.
Foiling is a process that uses heat, pressure, and dies. A sheet of foil paper is transferred to the cardstock by using heat and pressure of the die. The heat separates the coating of the foil sheets and the gold coating adheres to the cardstock by the pressure. This technique is a bit labour intense since it requires the operator to feed the foil sheets to fit perfectly over the die. The finish of this technique has a shiny appearance. Foil sheets can be found in various colours.
This process is completely different than foiling. This process is done with a printer that uses special metallic inks with particles of metal in the liquid of the ink. When the artwork is printed the ink dries leaving the metal pieces in the ink close to the surface of your cardstock. The dried metallic pieces will create a shine and also will reflect light. The labour is not as intense as the foiling and a metal die is not needed therefore leaving this technique to be half the price of the foiling technique.
Both techniques are beautiful , the differences between the two are the processes and the costs.