Even though, increasing the plating time to 45 min resulted in only a slight increase in the emissivity value, the appearance of the coating improved. Further increase in plating time was not beneficial since lipases gave powdery and non adherent coating. Hence the process time for black nickel plating was optimized at 45 min. Fig. 3 shows the effect of plating time on the IR emittance of the coating. Pictures of the coated substrates are presented in Fig.