Japanese Ceramic Rice Bowl

Japanese Ceramic Rice Bowl-This is a white ceramic bowl that measures 5 inches (12.7cm) in diameter and 2 ¼ inches (5.71cm) deep. There is a green 5-pointed Japanese star on the side of this bowl. It is marked on the bottom with a maker's mark and the number 28. I have been unable to identify what this means. This bowl has some discolorations inside, that appear to have been formed when this bowl was fired in the kiln. There are small bits of unrefined ceramic that can be felt under these dark spots. This bowl could be used in the mess hall but are unsure. Overall, it is in good condition.