The province of Siena is dotted with countless workshops because of its abundance of quality clay. Although not as high in iron as clay from Impruneta, clay from Siena is known throughout the world as quality terra cotta that can withstand temperatures to 14? Fahrenheit. A more refined clay, it is smoother in texture and great for Southern climates, indoor use, or in Northern climates if sheltered during times when temperatures drop below 14?.