Modern canvas is usually made of cotton or linen, along with polyvinyl chloride (PVC), although historically it was made from hemp. It differs from other heavy cotton fabrics, such as denim, in being plain weave rather than twill weave. Canvas comes in two basic types: plain and duck. The threads in duck canvas are more tightly woven. The term "duck" comes from the Dutch word for cloth, "doek". In the United States, canvas is classified in two ways: by weight (ounces per square yard) and by a graded number system. The numbers run in reverse of the weight so a number 10 canvas is lighter than number 4. Canvas has become the most common support medium for oil painting, replacing wooden panels. It was used from the 14th century in Italy, but only rarely. One of the earliest surviving oils on canvas is a French Madonna with angels from around 1410 in the Gemäldegalerie, Berlin.