U can make crackling effect by manual stroke
materials: oil paint for base color (inside the crack),water base paint(the one create cracks), blower,brush,sand paper
1st. u need to use sand paper to clean the surface of the area u want to paint then clean it with clean cloth
2nd. get the brush and use the oil paint in the surface (the thicker paint u put,creates big crack finish) wait for a minutes...it should be not wet but not totally dry
3rd. put the water base paint on top of the 1st coat (make sure all surface covered with paint) then use blower to dry u will see it will creat cracks.
i hope u can do it in proper stroke