Old-House Journal Online Navigation Bar

By Gordon Bock

The artful might want to explore highlighting raised ornament with a contrasting metal tone—either lightly brushed over a base color or applied first then exposed by a deft wiping.

Photo Courtesy of Gordon Bock

Hard to believe today, but a century ago radiators were cool-as stylish as they were high tech. Manufacturers cast each radiator body with ornate raised filigree, creating a ferrous canvas for the homeowner to complete to taste with paint. Metallic paint was assumed to be the perfect coating for radiators, and the decorative method most widely used was bronzing.

Bronzing is a traditional, easy-to-master technique that is still practical within limits for any old-house owner to employ today. A mixture of bronzing liquid (clear acrylic) and fine metallic powder, bronzing produces a richer finish in a wider range of colors than, say, simply spray painting from an aerosol can. Good, traditional paint or art-supply stores carry the powders in several shades of bronze as well as related tints. These can range from bright copper and brassy powders that emulate gold, to one or more aluminum powders that, once applied, shine closer to nickel or silver. All were available a century ago and are historically appropriate today.

Bronzing is not difficult, but neither is it particularly cheap in materials or time. A quart of bronzing liquid costs about $10 (not much more than quality enamel paint), but a pound of powder will set you back around $27—and you'll need the better part of a pound for the average-sized radiator. Add to your shopping list some sandable grey spray primer (choose the rust-resistant kind sold for autobody work) and a soft sable or camel's hair brush. The brush does not have to be special, but avoid the stiff bristles of paint or varnish brushes; they can leave streaks.

Not-So-Heavy Metal
Start with a clean radiator free of dirt and flaking paint. Stripping off built-up paint down to bare iron will maximize any cast ornament, but bronzing will cover just as well over a decent existing paint job. Either way, be sure to first prime any naked iron. Originally, radiator decorators used bronze primer made for the job or even just a coat of bronzing liquid served up neat (that is, without powder pigment), but autobody prime is fine. Heat-tolerance is not an issue, but you don't want to use anything water based that will, of course, rust the iron in no time.

Next mix up a batch of paint. Today as a century ago, the standard procedure is to start with a cup or so of liquid, then add powder until you achieve a mixture that is the consistency of cream—an odd metaphor for what looks like molten metal, but one that remains remarkably apt. Silver—that is aluminum powder—seems to go farther than the bronze colors, but in any event be prepared to use materials in roughly the proportions of one pound of powder to one quart of liquid.

Then simply brush on the paint. The actual bronzing demands anything but advanced skills; nonetheless, most folks develop a technique as they work on their particular radiator. Flowing on the liquid in a robust, but not too thick coat often produces a richer look than common brushing. Second coats in selected areas will smooth out sandy areas of the casting or create highlights on ornament. Period texts even advocate painting a radiator while it's warm to enhance the luster (a method uncorroborated for modern materials). The aesthetically daring or artistically inclined might even try bronze polychroming. Radiator companies of the past suggested going over the raised ornament on an already bronzed radiator with a stiff brush and complementary bronze in the following combinations:

  • Copper ornament on silver body
  • Silver ornament on copper body
  • Gold ornament on copper body
  • Gold ornament on blue-green body
Metallic Drawbacks
Bronzing is durable and gets a bit darker and mellower as it ages. Come to find out, though, the perfect paint for a radiator—at least as far as heating efficiency is concerned—is actually anything but metallic. In the 1920s, heating engineers took radiators into the lab to determine as accurately as possible what made the best coating for a radiator. In terms of physics, radiators heat a room though two modes: convection (heating the surrounding air) and radiation (heat energy emitted directly from the metal as waves). While tests revealed that radiator paint had no effect on convection it could dramatically influence radiation. As it turned out, only the last, exposed coat of paint had any impact and, among the oil-based paints tested, color made no appreciable difference. Ironically, metallic paints (and galvanizing) cut radiation by 7.4 to 9.2 percent.

So, if you're concerned about squeezing the maximum amount of heat out of your steam or hot-water heating system, you may want to think twice about bronzing. In the real world of old houses, though, there's more to the equation. Radiation accounts for only around 40 percent of the heat output of the typical radiator, and given that most turn-of-the-century heating systems are grossly over-spec'd by modern standards, you're probably not going to freeze as a result of a little bronzing—especially if you're not bronzing every radiator in the house. In fact, old-time heating contractors used to purposely bronze hyperactive radiators to moderate their heat output. Then too, if you're excited by the gleaming possibilities of radiators decorated with historically concocted metallic paint-not to mention restoring your whole house—are efficiency and saving a few pennies the only things that matter? Naaah!


Restore Media, LLC, is the producer of the
Traditional Building Exhibition and Conference and the publisher of Old-House Journal, Old-House Journal's New Old House, Old-House Journal's Restoration Directory, Old-House Journal's Traditional Products, Clem Labine's Traditional Building, Clem Labine's Period Homes, and tradweb—the Directory of Custom Building and Restoration Services.
Copyright 2007. Restore Media, LLC. All Rights Reserved.