Steel products may be coated with an insulating composition by a process which involves coating a uniform layer of finely ground glass powder on the steel and burning it at temperatures ranging from 700.degree.-1000.degree. C. Following, a paste comprising a mixture of the afore-mentioned glass, aluminum oxide and an evaporable liquid are deposited upon the burned coating, dried and burned again at 700.degree.-1000.degree. C.The resultant coatings adhere well to steel and resist temperatures as high as 860.degree. C., so suggesting then use for coating steel destined as a substitute for ceramic supports in electronic and hybrid microelectronic applications.