I'm doing an experiment to measure the Stefan Boltzmann constant with two small copper discs, one normal copper and one with a painted black surface. Both are covered with a a heated container and the termperature of the discs electronically measured. The black disc's temperature rises at a fairly constant rate, then tails off after a temperature rise of about 10 degrees. For the normal disc, a rise of 5 degrees was measured in the same time period and didn't tail off. My question is had I allowed more time for the normal disc, would it have reached the same temperature as the other did and then tail off, or will this temperature be different?