Bibi continues the Christmas chemistry series with ‘magic’ crystal growing…

In my quest for the perfect Christmas gift, I’ve come across some pretty cool (if sometimes geeky) stuff. Periodic table shower curtains and wall clocks where the numbers have been switched for element symbols are two examples; however, we have both in the office (the curtains are in the showers in case you were wondering…) and although they are practical, do the job and are chemistry related I thought I should find something a bit more exotic that involves practical chemistry. So the search continued.

Then I discovered the crystal-growing Christmas trees of the Natural History Museum (NHM). They pretty much do what they say on the box: you build a cardboard tree, put it in contact with a solution at the bottom which quickly moves up via capillary action and… hey presto, crystals grow on the branches creating the illusion of fluffy snow over the Christmas tree. The pictures below illustrate the process. 

 Interestingly, the chemical composition of the solution that forms the crystals is not specified anywhere. No reply was obtained from the manufacturers (see Update below) when I enquired and the box unhelpfully states ‘crystals are all around us and include salt and sugar’ so I decided to search elsewhere. A different website reviewing a similar (more colourful) product explains that the ‘magic solution’ is made up using table salt, water, ammonia and ‘Mrs Stewart’s liquid laundry bluing’.

I had never heard of such a reagent but a quick Google search informed me that Mrs. Stewart’s Bluing is ‘a colloidal suspension of extremely minute particles of blue powder [ferric hexacyanoferrate]’ that serves two purposes:

1. to provide colour to the finished product (alternatively this can be done using food colouring)

2. to provide nuclei for the salt crystallisation process

 The ammonia is simply used to speed up the evaporation process. No chemical reaction takes place, but I feel it is a great educational tool as children could be introduced to the concepts of evaporation and crystal formation, how this may be affected by the temperature of the surroundings, how the speed of formation affects the quality of the crystals, etc.  They also would probably be quite interested to look at the trees under magnification. 

If anything is slightly disappointing about this product it is the scale. I was expecting the trees to be a lot bigger, but they do not exceed 7 cm. On the plus side is the speed (I had crystal trees within 3-4 hrs) and the price (no more than £5). I could probably have blagged a free sample from the NHM with the excuse that I’m writing this blog and potentially promoting their product, but I decided to fork out the money and purchase my kit as the sales of this and other similar products support the museum. And that gets you Brownie points…

As a scientist, something I found strange is the following statement on the back of the box: ‘Since ancient times, crystals have been said to give their owners special abilities or healing powers.’ I wonder if the special abilities have anything to do with selecting the winning number for the Spanish lottery El Gordo tomorrow… Somehow I doubt it.

Bibiana Campos Seijo

UPDATE: The manufacturers, WOW stuff, have since replied to my query and confirmed that the solution is a mixture of potassium phosphate and water.

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