Magnesium sharpeners

Unfortunately I don’t know too much about chemistry. Even though the Bavarian school system provided me with 13 years of education [1]I think this has now been reduced to 12 years., the type of school I went to and the modules I picked meant that I only ever had one semester of chemistry – so please forgive me and correct me if I am using the wrong words in this blog post.

A few days ago I noticed that my magnesium sharpeners look pretty bad. The surface is now very rough, not shiny any more at all, except for some small areas. The sharpeners have been stored together with a silver plated letter opener I bought very cheap from The Pen Shop. A few erasers were also next to the sharpeners for a long period of time. I’m now wondering what caused the corrosion/tarnishing of the magnesium.

Maybe someone who knows more about chemistry can tell me what happened – so that I can avoid similar mistakes in the future.

Click to get a better look how the surface looks like now


My first idea what might have happened: A process similar to the one when aluminium is used to clean tarnished silver took place. The magnesium sharpeners kept the silver-plated letter opener untarnished, because magnesium is less noble than silver and therefore attracted sulphur or other chemical elements.

My alternative suggestion: Just like the chemicals from another eraser ‘ruined’ one of my wooden pencil boxes once, the chemicals from the erasers that were stored together with the magnesium sharpener changed the sharpeners’ surface, too.

Can anyone tell me what really happened to the magnesium sharpeners?


1 I think this has now been reduced to 12 years.

9 thoughts on “Magnesium sharpeners”

  1. I know very little about chemistry. But that happens to my magnesium sharpeners, too, and there’s nothing else metal in the box or case (save pencil ferrules). While I appreciate how pocket-friendly the light mag wedges can be, the dullness of magnesium after a while keeps my brass sharpeners in the rotation.

    I’ve had good luck cleaning mag sharpeners with a baking sode paste, but it doesn’t get them shiny again. It does get brass looking wonderful though, without the use of excessive cleaners.

  2. Thank you for your comment.

    I have another magnesium sharpener, stored in my pencil case, that is perfectly fine, so I thought it might have been the environment more than the age of the two pictured sharpeners.
    Are your sharpeners just dull or is the surface different, too. Mine have a sandpaper-like surface now.

  3. The latter. They look pretty chewed up. Because the metal is soft? (One of mine is missing a chunk my pal cut off with a pocket knife two years ago when we wanted to see if the alloy had enough magnesium to burn — YES!)

    Most mag sharpeners I’ve ever had looked pretty beaten up when I got them, unless they came in an individual package (rare I suppose). It’s more a matter of “wear” than the nice patina the brass sharpeners get.

  4. Mine pitted badly after just two months stored with a few pencils and erasers in a box. Last magnesium sharpener I will ever buy.

  5. Magnesium will oxide in wet or humid environments very quickly. The white powdery film is magnesium oxide, aka white rust.
    Store these sharpeners in a dry place and don’t store them as as sacrifices to other metals or what you got is what you’ll get.

  6. John, I did see a youtube video of a burning magnesium sharpener. Sounds like a jolly pastime.

    Kevin, those sharpeners I stored in a similar way to the way you stored yours seem fine …but the weather isn’t the same where you and I live and in my case the sharpeners are from another brand and might have a different composition. My surprise came because I have very old magnesium sharpeners that look perfectly fine, so I just didn’t expect these fairly new magnesium sharpeners to look like that already…

    John, thanks for the link. Oh, the shop you link to even ships to the UK – nice. Is this sharpener good? So far I wasn’t too lucky when it comes to sharpeners from KUM.

    Phil, thanks for this explanation. A quick look on the web seems to suggest that it’s possible to get rid of magnesium oxide with heat, but I guess that’s not something I should try at home ;^)

  7. Matthias, I suppose it’s as good as any other KUM wedge-type I own, which is to say, they take some getting used to. They are so aggressive when they’re new! But having extra blades with me is nice, especially on a trip or camp-out, though I shouldn’t admit to packing a sharpening to go camping when I already have a knife on me. 🙂

  8. Shannon jennings

    I can tell u the sharpener attracted the tarnish grom your silver. Kkind of like a ” sacrifitial metal” on a boat .

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