Recently I melted some (red) copper scrap which I poured into sheet blanks of 3mm thick and about 2"x3" size. I melted the copper under a few pieces of charcoal to prevent oxygen dissolution into the Cu metal. That worked, after wirebrushing the sand off the blanks I rolled them into sheet of less than a mm thickness with a few intermediate anneals. I used to cast sheet blanks in a steel mold which all times resulted in incomplete castings due to premature freezing. The sand castings appear to be much more succesful. Now I did the same with brass, by remelting scrap, including lathings. I also got the sheet blanks but after rolling down to 1.5-2mm thickness with one time intermediate annealing it cracked. I remelted the brass and casted the blanks again, but after rolling the cracks aooeared again. Weird, because brass contains zinc which prevents oxidation of the copper. What can be the problem here ?