noun [U]
1 a hard but delicate shiny white substance made by heating a special type of clay to a high temperature, used to make cups, plates, decorations, etc:
a porcelain dish
The tea cups are (made of) porcelain.
2 cups, plates and decorations, etc. made of porcelain:
He had a fine collection of Meissen porcelain.
china
noun [U]
clay of a high quality that is shaped and then heated to make it permanently hard, or objects made from this, such as cups and plates:
china plates
從以上這個解釋來看，
porcelain側重於工藝品類陶瓷作品,也是較為常用的"瓷器"的總稱
china則側重於非工業類(比如說日用瓷)