Why are barns red?

If you've ever spent much time in American farm country, then you've probably noticed that there's a strong tradition there of coating barns and outbuildings with red paint. Why?

Because nuclear fusion.

Okay, the actual answer is simply because red paint has long been a cheap color to buy. But, explains Google engineer Yonatan Zunger, there is some really interesting physics lurking in the background of that price point.

What makes a cheap pigment? Obviously, that it’s plentiful. The red pigment that makes cheap paint is red ochre, which is just iron and oxygen. These are incredibly plentiful: the Earth’s crust is 6% iron and 30% oxygen. Oxygen is plentiful and affects the color of compounds it’s in by shaping them, but the real color is determined by the d-electrons of whatever attaches to it: red from iron, blues and greens from copper, a beautiful deep blue from cobalt, and so on. So if we know that good pigments will all come from elements in that big d-block in the middle, the real question is, why is one of these elements, iron, so much more common than all of the others? Why isn’t our world made mostly of, say, copper, or vanadium?

The answer, again, is nuclear fusion.

You can read the full story on Zunger's Google+ page. In my experience, white is another really common barn color, due to the fact that whitewash — a paint made from calcium hydroxide and chalk (which is also calcium) — is way cheap, as well. Calcium is also one of the most abundant elements in the Earth's crust ... clocking in at number 5, right under iron in the top 10. I'm sure there's some different science that accounts for the high concentrations of calcium on our planet, but the same principal applies. Cheap paint is paint made with abundant (and easily accessible) elements. And abundant elements happen because of physics.

Image: Red Nebraska Barn, a Creative Commons Attribution No-Derivative-Works (2.0) image from 50779843@N03's photostream


  1. Cool. The joke answer is red is so cheap because all the farmers buy so darn much of it.

  2. I had heard they were red because animal blood (waste not, after a slaughter) was used as the pigment. 

    1. Animal blood wouldn’t stay red. If you’ve ever seen an old blood stain, it’s a very dark brown (actually caused by the oxidation of oxy-hemoglobin (HbO2) to met-hemoglobin (met-Hb)).

      In any case, if it were true, then the barns would be red for almost the exact same reason! Iron in hemoglobin reacting with oxygen, turning red.

      1. Yup. You *could* boil down and react animal blood in all sorts of ways to pull out a bit of red pigment, but it would be one hell of a lot of work; much easier to dig some of that red clay out of the ground. Or do virtually anything else.

        If you want to put surplus blood to good use, then using it to make blood sausage, etc., is generally a much better plan. :)

    2. Ox blood is traditional for treating the structural beams as it hardens the wood and increases its structural integrity. Maybe it makes sense to paint the exterior to match?

    3. If you waste not, want not, you use some of the blood for black pudding. Much tastier than paint!

  3. If it blended with the surroundings how else are we supposed to hit the broad side then?

    1. To bring this back full circle to nuclear physics… 
      The apparent size of a nucleus was given the unit of “barns” because the apparent size to neutron/etc is so much larger than the actual nucleus — thus hitting a nucleus was much easier than they expected aka easy as hitting the broadside of a barn…

      Barn (unit) – Wikipedia, the free encyclopedia

  4. My family home is on a piece of property that contains an old ochre mine.  It was a pit mine, abandoned when the water table came up and filled the pit.

    ochre is really an iron rich clay.  you could see the variations in the mine, everything from a yellow clay to dark orangish stone.  Not sure which grade they actually used.  I believe they crush and fire the harder grade to make it into a red power. 

    1.  Oh, I also wanted to say there is probably a second part to this answer.  Because it raises the question of “Why aren’t old houses all red?”

      The answer is something like this.
      1. Red paint was the cheapest
      2. people didn’t want to live in red houses (see references to blood above).

      1. (see references to blood above).

        Or it’s because they didn’t want to paint their house the cheapest color.

        There’s the old saying “too poor for paint, too proud for whitewash” — you could probably substitute “red ochre” for “whitewash.”

  5. Red from iron oxide not only because it is cheap and plentiful, but because it ‘wears like iron’.  White paint formula is lead-based, not to be confused with whitewash, which was made primarily from lye, the result of washing down the also-plentiful wood ashes.

    1. Actually, these days is white paints is mainly (AFAIK, IANAChemist) made from Titanium Dioxide, what with lead being so poisonous

  6. Early New England paint colors were red and white (as noted above), black (carbon from combustion), green (copper oxide), brown (from, well, mud) and mixtures of these. Yes, that means that pastel pink is a defensible house color, much as some historical societies wish it wasn’t.

  7. Also common, of course, were bare cedar planks/shingles, which weather to a lovely gray.

  8. ‘Because nuclear fusion.’ ought to be the answer to any question, with a long-winded explanation behind it. Suns gone supernova, where would we be without them?

  9. Growing up, I was told we painted the barns red not just because red was a less expensive paint but mostly because it lasted longer than any of the other colors.  Even as it faded, it still didn’t look bad.  The real expense wasn’t the cost of the paint but either paying the labor to paint the barn (by far the tallest structures around at that time) or taking time off from your own field work to get the barn painted.  A good paint job lasted 10 years or more.

    The most “expensive” colors were white and then black.  Again, because they had to be reapplied every 2 years due to fading and deterioration.   My grandfather would talk about how he had one of the first white dairy barns in the county…thus showing he was one of the most prosperous.  When his neighbor wanted to boast, he painted his barn black since white was all ready taken.  (BTW, being good, stout Germans, they never actually bragged.  They would simply state the fact that their barn was white/black and claim it had some benefit to milk production.)

    I don’t know anyone who used whitewash on the exterior.  I would think that would have to be re-applied too often.

    1. Good point. That ties into something someone asked on the OP, about why we used pigments in the paint at all — surely it would be cheaper to have a completely unpigmented paint, basically just oil the thing? My guess is that, if you’re already going to do the work to paint a barn, you may as well paint it a color that’s going to look good (and cover up imperfections) for some time to come.

      1. Pigments protect from UV degradation. Paint lasts a lot longer than any clear finish.

    2. I grew up in an area with some of the oldest extent barns in the country. and the older they are the more likely they are to be white. Particularly the Colonial buildings of all types. Obviously the farther back you go the less access there was to anything else besides white wash to paint your buildings. But I think more importantly white wash isn’t lead based, so those buildings painted with it were less likely to be repainted another color.

    1. There’s actually a great discussion in all of that — it turns out to involve special relativity. Gold is the first nucleus that’s big enough that the electromagnetic force between the nucleus and the electrons is significantly deformed by relativistic effects, and that manages to significantly bend all of the energy levels within the atom. The result is that the outermost electrons of Gold atoms have an energy gap between them which is perfect for absorbing blue light (rather than the UV light they would absorb without relativity), and so the light they reflect off is a wonderful golden color.

      If it weren’t for relativity, Gold would be silverish, much like most of the other transition metals.

  10. Homes back in the 1700s were much more colorful than people think.  People are given the impression now that all homes back then were white but in reality they were red, blue, etc.

  11. Originally, barns were natural and allowed to weather. Then along came “Wood Preservation” 

    American farmers began using homemade
    paints to preserve the wood for their barns. Ingredients such as lime, milk and linseed oil were used to make a hard paint that protected barn
    exteriors from natural elements such as rain, snow and hot summer sun.
    This paint could last many years.

    Why Red?

    Farmers had limited choices for paint colors.
    Most farmers made their own paints out of materials naturally available
    to them. For paint color, farmers used two things that they had a lot
    of on their farms: blood and rust. When farmers used blood from animal
    slaughter, the paint darkened as it dried. Rust was also used quite a
    bit, and the two shades were very comparable. Eventually, farmers came
    to believe that rust red absorbed more sunlight in the winter months,
    keeping the barn warmer.

    Pirated directly from E-How. **As an aside, when I was a kid in Britain, the hardware store had big bins of ‘black lead’, ‘white lead’ and ‘red lead’, which was mixed with linseed oil for paint. The colors could be mixed for tints and are recognized now as poisonous. My grandfather at the time was a painter and went into a month long lead induced coma.

  12. This is ridiculous.  Barns are red because people want red barns.  People wanted red barns because they had red barns in Europe—where the barn-builders came from.  The rest of the world had barns of a different color.

  13. Having been through a few murderous southern Minnesota winters, I’d like it noted that red is also relatively easy to see if you need to find a safe spot out there on the plains. If not a cause, at least an ancillary benefit.

    1. I can’t tell you how many times that I’ve gone into a barn only to discover both hammers and sickles.

    2. So Obama is behind this?

      But no, red barns predate Communism, so I blame expect… The Spanish Inquisition!

  14. No painters here, clearly. One of the biggest reasons for red pigment being cheaper is because it spreads much thinner and still produces an opaque coating. The pigment in paint, if opaque,  serves to absorb ultraviolet light thereby vastly extending the life of the coating. Red pigment, whatever it is (and I am betting it was never blood) always has the most opacity of any color. Equalling cheap in two different ways. Cheap to buy (just dirt) and cheap to use (goes a long way) bonus; paint lasts longer. All this from experience. Those guys didn’t know or care about fusion.

  15. Being a Reddleman back in the Middle Ages (a person who made red paint/dye and carted it around to sell to farmers so they could mark their livestock) was a “worst job” on Tony Robinson’s Worst Jobs in History. The Reddleman were themselves stained red from making the paint and were frequently treated as pariahs because of their resemblance to the devil.

  16. I’m curious how much of this comes from the Scandinavian preference for red farmhouses and barns (the famous Falu farg red paint, from Sweden’s massive copper mine)… A lot of these look awfully like those Minnesotan barns. http://bit.ly/10InDjb

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