A crackle finish can be achieved with the use of a very old product called hide glue.  Hide glue (yes, animal hides) is most often used as a furniture adhesive but has also been used for years by professional faux finishers to create a crackle finish.

Paint your object with a base coat of a color that you want for the cracks.  Dry.  Then paint on heated glue right over base coat.  Glue can be heated SLOWLY for ease in brushing by placing the glue can in heated water or a crock pot.   BE CAREFUL NOT TO OVERHEAT!!!  GLUE MAY EXPAND IN CAN AND BURST OR SPLATTER.   Allow to dry tacky.  Paint with selected color for outer color.  The more that the glue dries the smaller the cracks!!

For a source of "Hide Glue", go to Bjorn Industries     Also visit Lisa's website