Seasoned cast iron pans have a high emissivity coefficient. In response to thermal radiation, surface temperature depends on the thermal emissivity of the material. Each material has a different emissivity, which may vary by temperature and infrared wavelength. The higher the emissivity, the greater the emitted radiation at that wavelength. For aged conductor, the emissivity for heat radiation and the absorption of sunlight increases. Therefore, it is possible to create visibly dark colored surfaces with low thermal emissivity. The concept of emissivity is important in understanding the infrared emissions of objects. A polished silver surface has an emissivity of about 0.02 near room temperature. At any specific wavelength, reflectivity=1 - emissivity. The object's known temperature can then be measured using the standard emissivity. This "naturally" low thermal emissivity is found in some formulations of borosilicate or Pyrex. By definition, a black body in thermal equilibrium has an emissivity of . A shiny metal surface has low emissivity. Silk has a high emissivity for infrared light, making it feel cool to the touch. A major consideration is the low emissivity of yttria, which limits background radiation upon heating.