13
STEP 7:
Tie the other end of the line
around a ruler so that you can hang the
crystal completely in the alum solution.
You can use a pencil or chopstick (or sim-
ilar) instead. Do not let the seed crystal
touch the sides of the jar or the bottom
of the jar, as this will affect the crystal’s
shape.
STEP 8:
Cover the jar again with your pa-
per towel and rubber band. Place in a safe
spot, out of the way where it can grow for
many days.
STEP 9:
Wait for at least a week. The
longer you wait, the larger the crystal will
grow. If you see small crystals starting
to form on your jar, take out the crystal
on the fishing line, place it back in the
cleaned first jar, and pour the alum solu-
tion back in that jar as well (a fine screen
might help). Don’t let any of the small
crystals get in, because they will compete
with your big crystal for alum and it won’t
grow.
Scientists call alum a hydrated
potassium aluminum sulfate,
with the chemical formula
KAl(SO
4
)
2
*12H
2
O. That means it
has a potassium atom, K, and an
aluminum atom, Al. It is a sulfate,
which is sulfur and oxygen, and it
is hydrated, meaning it has water
molecules, in this case, twelve.
Alum was used by the ancients
to purify water, because it at-
taches to silt and solids, which ei-
ther float or sink. Today, it is used
to stop bleeding, in deodorants,
and for pickling. It is known as
Fitkari
in India and
tawas
in parts
of Asia.
Alum can grow into large isomet-
ric crystals that resemble two
pyramids stacked at the base.
As long as fresh solution contin-
ues to flow into an area where
crystals have started, crystals
can grow. It is a simple crystal to
grow at room temperature, and
its faces can make attractive,
inexpensive jewelry.
THE SCIENCE
BEHIND
THE FUN
Creative Enrichment
1. Try using thread and growing
tiny crystals all along its length.
2. Try altering the cooling rate
by adding ice cubes, setting
the cooling jar in a bath of ice
water, or keeping the solution in
a saucepan and leaving it on the
stove at a very low heat.
3. You could also grow a crystal
without the string, just by let-
ting it sit in the solution.
4. Try adding some glow-in-
the-dark liquid from a yellow
highlighter to your solution to
make a crystal that glows under
UV light.
