Glass
is
all
around
us
.
You
?
ll
find
it
in
windows
,
light
bulbs
,
mirrors
,
cars
,
and
cell
phone
screens
,
among
other
things
.
Yet
we
____________________
stop
to
think
about
this
amazing
material
.
What
is
glass
?
And
how
is
it
made
?
____________________
3500
BC
,
people
were
already
using
____________________
quartz
to
make
glass
in
ancient
Egypt
,
and
the
science
behind
glassmaking
hasn
?
t
changed
all
that
much
since
then
.
The
modern
glassmaking
____________________
involves
heating
tiny
crystals
of
quartz
,
more
commonly
known
____________________
sand
,
just
like
the
kind
you
?
d
find
at
the
beach
,
to
a
very
high
temperature
.
____________________
on
the
____________________
of
sand
and
other
materials
,
such
as
limestone
,
different
types
and
colors
of
glass
can
be
created
.
High
temperatures
are
required
because
sand
melts
____________________
around
1
,
760
degrees
Celsius
.
When
melted
sand
cools
,
it
doesn
?
t
turn
back
into
sand
.
It
is
____________________
into
a
completely
different
state
?
something
between
a
liquid
and
a
solid
.
This
molten
glass
is
then
____________________
into
molds
to
make
bottles
or
containers
,
or
it
is
poured
into
a
____________________
metal
bath
,
where
it
floats
on
top
to
form
sheets
of
glass
for
windows
.
Unusual
glass
containers
and
art
are
made
by
glassblowing
,
which
is
the
act
of
shaping
glass
by
blowing
air
into
molten
glass
.
Glass
is
a
common
construction
material
because
of
its
unique
properties
.
For
example
,
it
?
s
transparent
,
yet
it
?
s
strong
enough
to
resist
the
elements
.
Here
are
some
fun
facts
about
glass
.
Natural
Glass
Some
glass
is
naturally
formed
by
the
____________________
of
volcanoes
.
Our
____________________
used
this
glass
to
make
knives
and
jewelry
.
Recycled
Glass
Glass
can
be
recycled
repeatedly
without
losing
quality
,
and
it
?
s
one
of
the
easiest
materials
to
reuse
.
Most
new
glass
contains
some
amount
of
recycled
glass
.
Windshields
Car
windshields
were
____________________
made
with
regular
glass
,
which
could
shatter
and
cause
harm
in
the
event
of
an
accident
.
As
the
story
goes
,
car
manufacturer
Henry
Ford
himself
was
hurt
by
broken
glass
in
an
accident
and
was
motivated
to
find
something
better
.
In
1919
,
Ford
?
s
company
was
among
the
first
to
use
a
special
,
stronger
type
of
glass
for
windshields
.
Luxury
Windows
Glass
windows
have
only
been
common
since
the
seventeenth
century
.
____________________
____________________
,
they
were
seen
as
a
luxury
for
the
rich
.
Humans
have
been
making
glass
for
thousands
of
years
.
Today
,
a
huge
range
of
everyday
items
are
made
with
glass
.
____________________
it
?
s
used
in
____________________
or
to
make
works
of
art
,
glass
is
a
remarkable
material
and
one
that
should
definitely
not
be
____________________
!
