Modern engineering methods of calculation of heat exchange by radiation in flame heating furnaces are based on utilization of information on the radiant characteristics both of the medium filling the working space and of the refractory lining surfaces bounding it. For example, with use of the "balance-flows" method for calculation of radiant heat exchange [i] it is necessary to have available the values of the integral degree of blackness of the lining surface and its temperature.The use of a model of heat exchange with numerical solution of the integrated equation of radiant transfer also rests on knowledge of the integral degree of blackness of the lining surface [2].