A pen is an everyday item, found in a myriad of colours and for all uses. But what if I
told you that black ink isn’t just black; or brown isn’t brown.
In many pens the ink used is a mixture of chemicals that are brought together to achieve
the desired colour and consistency,
relying on the use of primary colours (blue, green,
red) to generate all the others.
We can study the contents of different inks using a technique called chromatography, literally
“drawing a colour graph”. Chromatography is the science of separation and is used in
the chemical industry in many forms from purifying chemicals in a reaction, studying the contents of water,
to testing for the presence of illegal compounds in athletes.
Compounds in a mixture will interact with a liquid and an absorbent material in different ways,
allowing for separation to occur.
In the same way that scientists can separate
and study 100’s of chemicals in the human
body we can turn the black ink into its components
So why don’t you give it a go for yourself?
To do this you will need the following:
• A pencil
• Some felt-tip pens of different colours
• A jam jar
• Roughly 10 to 15 cm tall
• Some coffe filter paper
or heavy tissue paper that'll act as the absorbent
• Some sellotape
• Some scissors
• And finally some water
Cut a strip of the coffee filter, or similar paper, a little longer than the height of your jar
and about 20 mm wide. Draw a pencil line across the strip about 10 mm from one end of the paper.
Fold over the other end, and staple it into place
around the pencil.
Draw a small blob of ink with the felt-tip pen on the pencil line.
It’s best to go over this blob several times to get as much ink on it as you can,
but don’t let it get more than about 2 mm in diameter.
Next thing to do is to fill your jar with water.
About half a centimetre would do.
Once you're ready
Drop your paper, careful to make sure it doesn't touch the bottom.
or the sides.
and now we wait
As the experiment runs over a few minutes
you should beging to see different colours appearing
in the moving water front
as the different pigments in the ink separate out
we can start to see here
a splash of a yellow
yellowy brown maybe
and blue
The next thing we do, is just draw a line to show where the waterfront ended
So let's look at our result
Our rink has been separated into lots of different colours
we have some yellow down here.
and maybe some hint of a brown,
the black in the middle is because we put a lot of ink on.
but up here we can see that our black is also containing purple
light blue
and some dark blue
you might like to repeat this
to try the effect of different sized spots of ink or
or different colours
we can see our black here
which is the one we've just done
but this is the green which appears to be made up of green yellow and blue
or blue, which appears to be made up of purple, light blue, and blue itself
or the red
which appears just to be red
Get more from The Open University
Check out the links on screen now.