What type of ink is used in hp #21 & # 22 cartridge ie.., an ordinary pen ink or an special type of ink?

In hp printers the cartridge nos #21(C9351G) & #22 (C9352G) an ink of black & tri -colors are used what type of ink is used in it, If any one knows the answer, Plz Cont: "drag_the_hot@yahoo.com" & "govindarajkarthikeyan@gmail.com"