Jdurg is, of course, the expert here, but from my experience I have found that mineral oil is really not sufficient for keeping sodium metal nice and pretty.  I keep a small amount on my lab bench in an identical vial.  I have found that the stuff tends to only last a few months before it starts to turn white (NaOH).  I would say that if you really want to keep it nice you would need to keep it in a sealed ampoule.  You could probably extend the life in that vial by trying to seal it with Parafilm or maybe even wax to prevent oxygen and water from getting in.  Be careful though, those caps tend to corrode over time too.

Thanks for your reply, both of you. Your answers are clear and I'll see what I can do to keep this sample nice and shiny. I'll store it in another tightly capped bottle, just a little larger than the one, shown on the site. At least, that creates another barrier for oxygen and water vapor to come in. If I want to show it to someone, then I'll take it out, realizing that every time I show it, a little new oxygen ccan enter the larger bottle...

A little bit late for a reply, but I just returned from my holidays...

The sodium I have still is as nice and shiny as when I received it. I'm also considering the purchase of a small sample of potassium metal, but the stories about peroxide-forming and the risks of explosion scare me away from purchasing potassium metal. I also would like to have some for experimenting (just as I have for sodium, 1 bottle as collector's item, the other for experiments). If I read about the troubles with the storage of the potassium, then I think that the alkali metals will be represented by a single member, being the sodium metal. Maybe, I buy a compelely sealed sample in argon gas, but unfortunately, these are much more expensive.

I also purchased 75 grams of calcium metal and I received it today. The metal is in a completely sealed metal tin, which, once opened, cannot be closed again. I still left the container closed and before I open up the container, I would like to know what is the best method of storing the calcium metal.

Several years ago, I also had a chunk of calcium metal, which I stored in a glass bottle. A few months later, I only found a white powder of calcium oxide and carbonate, so this should not happen again. Must calcium metal be stored under mineral oil as well or can I store it under ligroin with a low boiling point? Any advice on this would be very welcome.

What I'm wondering about is the colors of the oxidation layers of the different metals. Sodium metal is covered by some white layer, which is perfectly understandable, because Na2O and NaOH are white. If I look at my praseodymium sample, then it turns black, but also with some green specks. The green color is understandable, it is the color of Pr2O3, but what is the black stuff? The same thing for calcium. Calcium oxide, hydroxide and carbonate all are white, so what can explain the dark grey/blue or even grey/black color of the sample of calcium, which I have.

You mention that your K-sample is somewhat purple (I checked your picture and indeed it looks somewhat purple) and now also turns orange. The orange color is understandable, but what it the purple stuff?

Etc. etc. with other metals, I simply do not understand the colors of the oxidation layer on the metal.

I have been able to obtain some potassium metal, but I am a bit worried by jdurg posts concerning the stability of the superoxide...

The situation is, that I bought the potassium with a whole lot of other chems, in an all-in-one sale, this was a couple of month's ago, and now I am going abroad soon for my MSc, and I want to store it responsibly, so no strange things can happen to it...

I've made some fancy pictures (clickable), which are below:
This photo is of the largest chunk there is in the bottle.


This is one of the few chunks with an orangish spot on it, it looks like it's taking over the chunk.


This a shot of hte 100ml beaker I put all the chunks in, I did this because I couldn't see the colour properly through the amber bottle the originals were.


After I put the small chunk back into the oil, it started to release bubbles I was rather scared, and transferred the chunk as quickly as possible to a separate container with oil. Fortunalty no runaway reaction happened. Here is a photo of the event, just before I transferrred it:


So my question boils down to: What should I do with this stuff? I would love to keep some, as potassium is a rare element, and is not very easy to get.
However, I have my resposibility, and when I leave I will come back only once in the 3 month's, íf even that often.
What are the risks of cutting the oxide layer off under a massive layer of oil, is there ANY chance that it will ignite when the K2O2 gets rubbed into the potassium metal by the action of cutting?

Jdurg, thanks for you compliments and the warm welcome!

Please don't bother to clean all the pictures up, I've made some in good ol' sunlight.
They are below, the photo was made after work, in a Dutch summer/autumn sun, around 5pm.
It isn't too sharp, but the colours are much better, though the oil has also already a bit of a yellowish shine.

Unfortunatly I do not have a special vacuum bottle, however, I could make some very dry oil/solvent with anhydr. MgSO4, filter, add in a 100ml RBF, add potassium chunks, pull vacuum, release, gently not creating bubbles, flush all the oxgen out of the above air layer (I have an aerosol can therefore), and stopper it. Maybe that is a way forward.

The pieces with orange are indeed applying for a single trip to a large amount of water. Is a nice project, and íf I do it, I will try to catch it on tape and post it if anybody is interested...

Ok, the pic, here it is:


I know I can't do anything with the potassium, but it just doesn't feel good to chuck it all away, but maybe it is the best option.

BUT, if you think of the peroxidised parts of it, if it reacts under a few cm of oil with the K, and there are signs of fire, like a spark or something, to which extend would that be dangerous? The oil is plain parrafin, and cannot burn without oxygen, so there is simply no other oxygen there than is present in the K2O2 form... so under a large layer of oil, (I say large, I mean large, something like 10-15cm in a 600ml beaker)  it should be able to abuse the chunks severely without any harmfull consequense for the experiment executioner, shouldn't it?
what do you think? It is handy nor easy to cut with a long knife under a large layer of oil, with a breaking index which is probably going to make you seesick, but I have done worse things...

What methods do university laboratories use to maintain a long shelf life of the alkali metals such as potassium, sodium, and lithium? I can not believe that they maintain them in oil in a vacuum chamber.