Complex sentence: Panel painting was a painting support medium in popular use in the West for about 300 years--from the late 12th century until the use of canvas and oil paint became the norm in the 16th century.
Split into simpler sentences: Panel painting was a painting support medium in popular use in the West from about the 12th through 16th centuries. The use of canvas and oil paint did not emerge in popular use until the 16th century.