When did madame cj walker invent the pressing comb?

Madam C. J. Walker did not invent the pressing comb. This is an inaccurate myth which many people keep repeating despite evidence to the contrary. Heated hair care implements were in use as early as the 1870s in Europe when Madam Walker was still a child. If you google hot comb or straightening comb you'll find websites that give more information about people like Marcel Grateau, a Frenchman, who created the Marcel Wave.