Tom Winslow, Park Ranger/Education Specialist at Morristown National Historical Park, writes, “Another comment visitors often make is that the purpose of the cast-iron fireback in fireplaces was to reflect heat. Yet I have heard some people say that the primary reason was (in the days before firebrick) to protect the bricks in the hearth from damage due to high temperatures. is it one or the other . . . or all of the above?”
Surprise! (To me, at least–I thought protect-the-bricks sounded like a myth.) There are no myths here. Both statements are true.
One purpose of a cast-iron fireback was to absorb the heat and radiate it into the room. It also offered some protection to the bricks behind it.
In his 1927 book, Iron and Brass Implements of the English House, author Seymour Lindsay writes,”The chief drawback to the early wall down-hearth was the destruction of the back wall of the hearth opening caused by the fire. So great was the damage in larger fireplaces, that the back wall had to be refaced from time to time. This difficulty was overcome with the introduction of cast iron, which lead to the production of large thick plates of sufficient strength to resist the heat. These ‘fire plates’ or ‘fire backs’ are still to be found in great variety throughout the country.”
But here’s what clinched it for me: Chambers Cyclopedia (1753) defines a fireback: “a large plate of cast iron, frequently adorned with figures in low relievo, serving not only to preserve the stone work of the chimney back, but also to reflect the heat of the fire forwards.”