I can give few thumb rule for differentiating blow hole and shrinkage.

Blow hole generally single hole,where as shrinkage will be single hole Surrounded by cluster of hole,Shrinkage genrally appears in thick section.Shinkage can be eliminated by using exothermic sleeves. 

hi

In generally blow holes are comes due air, holes are generate in form like bobble. but shrinkage is reduction of volume or area from the expect  . no need to  test EDS for find holes and shrinkage. EDS is generally used for finding the composition of the materials.SEM is used to find blow holes and clusters and particles etc. if want to get how accurate surface structure use FESEM.

Blow holes are having irregular voids but shrinkage has laminar layer and sometimes this may also create big voids with good inner surface finish. Using EDAX/EDS, we can identify the composition without recognizing the defects like shrinkage/blow holes...

blowholes are larger gas bubbles and related to inability of decomposed core and mold gasses