Descaling is the process of removing limescale, which is principally crystalline calcium carbonate, from whatever it has formed on. It is usally done with a descaling product, which is a mild acid solution. For industrial/commercial contexts like hot-water pipes there are modern methods involving alternating magnetic fields for dealing with limescale. But if you live in North America you are probably blissfully ignorant of the whole process.

Backstory: Years ago, in my senior year in college I took my first step into my adult life of material posessions and bought my own coffee maker (hey, I was writing a thesis on top of a full courseload). Wanting to acquire not just a coffee maker but a fetishistic machine for caffeination, I went European: I bought a top-of-the-line black, sleek looking one made by Braun. It had a wonderful name like the "Brewmaster 2000" or some such thing. As I was reading the instructions, which come in a big booklet translated into maybe eight languages, I got to a section on how to "clean and maintain" the coffee maker.

The instructions were all more or less common sense until I got to a bit about descaling. It was kind of alarmist. In my head it went like this: after every few months of normal use you MUST RUN A WEAK VINEGAR SOLUTION THROUGH THE MACHINE, or use a commercial descaling product, or the heating mechanism will gum up and the pipes will clog and you'll won't have any coffee, and you'll never finish your thesis, you ignorant slacker.

After I shuddered a bit at the prospect of not graduating, I then remember thinking: commercial descaling product?

Needless to say I got busy with classes and writing, the coffee flowed freely and I forgot all about the dire Germanic warnings of doom. In fact, I had that coffee maker for seven more years until a dear friend recently replaced it as a wedding present. It was indeed kind of tired, and the plastic filter basket had started to degrade and warp from years of heat, but the water ran through with no problem, despite what the instructions had said. So I'd figured: crazy, paranoid Germans.

Just before that, though, I had moved to London for a year (up until now this was all happening on the east coast of the U.S.), and I realized what Braun was talking about. Much of England is made of limestone, which is just chock full of calcium carbonate, the principal stuff that goes into limescale. So the tap water has, shall we say, more than a full day's supply of dissociated calcium salts floating around in it. Everywhere I had ever lived before, whenever you left drops of water from the faucet in the sink or spilled a bit on the counter it would just evaporate away, and that was that. We were there inside of a week when we noticed that wherever water was left to evaporate a deep, chalky-greasy buildup of white gunk would form. Worse, once it had formed it was like a kind of armor: you had to really scrub away at it with hot water and soap to get it out. Finally after a few weeks we had an ex-pat frend of ours over, and we complained about it. She said, "Oh, which descaling product do you use?"


Turns out there is a whole section in the grocery store for descaling. Calcium carbonate is heavily alkaline, so most of these products are basically just acids with a little soap and blue dye. Without them you just can't get the stuff off. In fact, all the window cleaning and general-purpose stuff ("Windex", etc) is all vinegar-based (an acid) instead of ammonia-based (a base) because ammonia is almost useless against limescale. This is also surreal, because as an American I had come to associate the smell of ammonia with squeaky disinfected cleanliness, and the smell of vinegar with, well, salad dressing. I never did get to the point where I could walk into the kitchen, soak it down with salad dressing and then go: *sniff!* Boy it smells *clean*!

Aside from sparkling kitchen fixtures this is also a serious problem with pipes and water heating, which is what the Braun people were talking about, because of a funny chemical property of calcium carbonate: it's solubility decreases at higher temperatures. This means that whenever you pass it across a heating element it becomes more likely to form little rhombohedral crystalline deposits on said heater. Eventually the coating decreases the efficiency of the element so much that it no longer works; copper is roughly 500 times more conductive than calcium carbonate (0.8 W/m K vs. 393). The precipitation reaction looks like this:

Ca+2 + 2HCO3- ==> CaCO3 + H2CO3

The calcium salt then sticks to the metal surface through electrostatic attraction, and crystals begin to grow.

This is made all the worse because while it is a perfectly reasonable thing to soak my kitchen, bathtub and coffee pot down in acid once in a while, it's not something you can do to the tap water systems of an apartment building without poisoning the neighbors. Luckily, modern science has recently come up with a promising answer: electronic descaling technology.

Electronic descaling (sometimes called "magnetic descaling") works like this: a solenoid cable is wrapped around a set of piping. The current is made to alternate in such a way that a time-varying magnetic field is produced, which induces an alternating electric field (via Faraday's Law). The alternating field causes the calcium salts to collide and precipitate in solution, since negative and positive ions are drawn in opposite directions and bash into one another. If this is done before water reaches the heating element, the precipitate zooms by it without forming deposits. Of course, that means that there's a little more calcium that's going to end up in dried up pools on your countertop.

But don't worry. You've got descaling products.