Spread porosity

It only goes to show you that casting is not a science but a black
art. I believe that oxygen is absorbed into the metal when it is
overheated thus expanding the sprue button. I don’t know much about
metal structure, etc only what I have experienced. I have had only
one very bad experiance with porosity. Someone told me that I was
pouring metal in to a mold that was too cold. Thinking that what I
had been doing sucessfully for about 10 years was all wrong I poured
ithe metal into a much hotter mold. The sprue button blew up like a
sponge. I cut the button in half on my band saw and found the
insides looked like a sponge. I have noticed that there are almost
as many opinions on how to do things as there are artists.
Lee