With the start of cooling when the formation of carbon oxides and steam is practically finished, there is a reduction in the solubility of the hydrogen in the steel. As a result of the process; the birth, growth, and breaking away of the bubbles are prolonged into the cooling stage after firing of the steel with the applied enamel, but at this stage also on account of the hydrogen. With further reduction in the temperature the separation of hydrogen is continued, but there is also an increase in the viscosity of the molten enamel. In this case, at a certain temperature, the viscosity increases so much that the hydrogen is in no state to overcome the resistance of the coating layer. The growth of the bubbles already existing is discontinued~ and the hydrogen remaining in the steel cannot contribute to the formation of new bubbles, although its separation continues. As a result, after cooling the system to room temperature such a pressure is created within certain bubbles and microcavities contacting the steel, that it leads to the defect of fish scale (according to the well-known theory). Hence, it can be concluded that the tendency of any system to develop fish scale depends on the temperature at which the growth of bubbles is discontinued -- the "freezing" temperature. The higher this temperature, then, the more hydrogen remains in the steel, other conditions being equal, and the greater the probability of defect formation. We developed a method of experimentally determining the stated temperature. The essence of the method consists in using the so-called secondary boiling. If the steel, cooled after firing with the ground enamel~ is heated again to the "freezing" temperature then the bubbles existing in contact with the steel and having excess pressure will cause an increase in the pressure. In practice the determination can be made with the equipment described in [2] or equipment similar to it.