Shrinkage porosity (dendritic porosity) is usually angular in shape, can be large or small and is
usually seen in patches in the heavier areas of the castings.
Please check:

1. Check the sprue placement on the casting. Sprues should be placed on the heaviest area of
the casting to allow progressive solidification of the metal.
2. Check the size of the sprues on the castings; they may be undersize for the size and weight
of the casting.
3. Avoid pinched sprues or narrowing of the sprues at the attachment areas of the casting.
This is a very common cause of shrinkage porosity.
4. Check the size of the main sprue rod on the cast trees; it may be too small for the size of the
tree being cast. The main sprue rod is a reservoir of fresh metal and heat to feed the castings
as they solidify.
5. Check the flask temperature being used; it may be too hot for the size and weight of the pieces being cast.
6. Multiple sprues may be needed on some delicate or thick – thin– thick designs to provide
a better feed and avoid shrinkage porosity.