Candy Glass
Fiber Drawing Using the Double
Crucible Method
By Tara Schneider
Summer 2005
Advisors: Bill Heffner and Himanshu Jain
IMI-NFG at Lehigh University
Work Supported By NSF’s International Materials Institute for New Functionality in Glass
Introduction
This slide show includes background
information on optical fibers, Snell’s Law,
and glass science.
 At the end of the slide show is a lab that
can be performed using ingredients and
supplies you can find in your kitchen.

Fiber Optics
Background Information

The following topics relate to fiber optics:
– Core and Cladding
– Total Internal Reflection
– Uses
– Comparison to Wires and Current
Core and Cladding
A fiber optics cable is a
long string of glass that
consists of a core and a
cladding (Picture). The
cladding surrounds the
core and has a lower
index of refraction, n.
The core can transmit one
or more colors of light.
Total internal reflection in
the core keeps light from
escaping.
Cladding
Core
A slice of a fiber optics cable.
Note: In our experiment, we create a
fiber optics cable with a core and a
cladding to demonstrate the double
crucible method. The core and
cladding do not have different indices
of refraction, n values.
Snell’s Law
What is total internal
reflection (TIR)? To
understand why TIR
occurs, one must know
Snell’s Law.
 Snell’s law states:

• n1sinθ1=n2sinθ2 (see
diagram).
• The reflected angle equals
the incident angle. θ1=θr
 Note: The dotted line is the
normal. All angles are
measured from the normal.
Total Internal Reflection
Keeps Light in.
n2
θ2
n1
θ1
θr
Reflection and Refraction. n1>n2
Total Internal Reflection



If θ2 is greater than 90° then
no light is refracted. The
incident angle that would cause
this 90° angle of refraction, θ2,
is called the critical angle, θc.
n1sinθ1=n2sinθ2 becomes
n1sinθc=n2sin 90°.
So the critical angle is
sinθc=n2/n1
Total Internal Reflection
Keeps Light in.
n2
n1
θc
θr
Critical Angle and
Reflected Angle. n1>n2.
Uses

Fiber optics cables can
be used for the
following applications:
– Communication
 Telephone
 Television
 Internet
– Surgery
– Toys
– Uses yet to be
imagined!
Fiber Optic Fish.
Photo courtesy of Robert Backman.
“Fiber Optic Cable.”
18 April, 2002. Online Image. www.accs.net /users/kriel/ch12 notes/. 4 August, 2005.
<http://www.accs.net/users/kriel/ch12%20note
s/fiber_optic_cable.jpg>.
Comparison to Wires and Current
A wire can transmit current, either in a positive
direction or a negative direction.
 A fiber optics cable can transmit light in two
directions at the same time. It can also transmit
light in different phases, amplitudes, and
sometimes different colors.
 Optical fibers can carry more information, and
they can carry it a farther distance than wires.

Glass

Topics covered include:
– Crystalline and Amorphous Solids
– Supercooled Liquid and Viscosity
– Glass Transition Temperature
– Fiber Drawing
– Similarities Between Candy and Glass
Crystalline vs. Amorphous
Most solids are crystalline, but glass is
amorphous. Glass does not have a repeated
molecular structure.
 An amorphous solid resembles a liquid frozen in
time.

“Molecular arrangement in a crystal.”
No
date. Online image. http://math.ucr.edu/. 3 August, 2005.
<http://math.ucr.edu/home/baez/physics/General/Glass/glass.html>.
“Molecular arrangement in a glass.”
No date. Online image. http://math.ucr.edu/. 3 August, 2005.
<http://math.ucr.edu/home/baez/physics/General/Glass/glass.
html>.
Crystallization and Glass Forming
If you heat a crystal up to above the melting
temperature, Tm, and then cool it, it might
become a crystal or it might become a glass.
 If given enough time, the melt will become a
crystal. The molecules rearrange into their
lowest energy states which are very ordered.
 If you cool the melt quickly, it will not have time
to rearrange to become a crystal. Instead, it will
become a supercooled liquid, on its way to glass
formation.

Viscosity
Viscosity is the resistance to flow. A
highly viscous material flows slowly like
honey, and a material with low viscosity
flows easily like water.
 As this supercooled liquid becomes cooler
and cooler, the viscosity becomes greater
and greater.

Tg
(tē-jē)
When the viscosity becomes so high that
the material behaves more like a solid
than a liquid, it has become a glass. It
has hit Tg.
 Tg is the glass transition temperature. Tg
is lower than the melting temperature, Tm.

Fiber Drawing
In the experiment, we will draw fibers from a supercooled liquid.
Video will run after download – please be patient.
Candy Glass

Similarities between Candy and Glass
–
–
–
–
Amorphous solids
Tendency to crystallize under certain conditions
Glass former: SiO2 (Silicate) for glass, C12H24O12 (Sucrose) for candy
Glass modifier: Na2CO3 for sodium silicate glass, H2O for candy, reduces melting
temperature and decreases chemical durability
– Other stuff: Corn syrup reduces crystallization in candy. Dr. Jain’s paper says
that adding stuff to glass can increase glass forming ability. (Source: Jain, Himanshu and Isha Jain,
“Learning the Principles of Glass Science and Technology from Candy Making.” Lehigh University. No Date. Lehigh University. 5 Aug. 2005
<http://www.lehigh.edu/~inmatsci/faculty/candy_making.pdf>.) Note: Corn syrup is made of simpler sugars
than sucrose. Sucrose is fructose C12H24O12 and glucose C12H24O12 bonded
together. Corn syrup is fructose, glucose, water and other stuff which the Karo
company does not disclose.

Differences between Candy and Glass
– Candy will decompose (C12H24O12 bonds will break) at a temperature that is very
high or when not much water is present (Source: Jain, Himanshu. Personal Interview. June 2005.)
– Melting temperature Tm and glass transition temperature Tg are much lower for
candy than for glass.
And Now for the Experiment
Set-Up
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Supplies
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A stove or hot plate
Oven mitts
Two 600 mL beakers
Two thermometers that can read 144.5°C
410g sugar
240g corn syrup
100g water
Food coloring
Two glass funnels-the shorter the stem the better
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A
A
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 Outside funnel: Stem diameter ≈ 1.4cm
 Inside funnel: Stem diameter ≈ .7cm, preferably longer than stem of outside funnel.
clamp to hold the funnels, paper towel to protect funnels from scratching.
scale to measure ingredients
metal tray to catch hot candy and store fibers
glass rod to draw fibers with
reflection microscope
razor
Supercool Set-Up

Set up funnels as shown:
– Place paper towel between
the clamp and the funnel.
– Make sure the funnels are
concentric at the top and
bottom of the stem.
– Set it up so that the inside
funnel sticks out a little bit
at the bottom (this will help
you see if the cladding is
surrounding the core on all
sides).
– Is anything going to get in
the way of you pouring
your supercooled liquid?
– You will have a little time
during cooking and the
beginning of the pour to
make final adjustments.
“Double Crucible” Set Up.
June 2005.
Concentric
Funnel
Stems.
June 2005.
Procedure: Fiber Drawing
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You have the cooking mitts for a reason! Don’t get burned.
Measure 205g sugar, 120g water and 50g corn syrup into each
beaker. Stir before cooking but not during cooking.
Cook on a high setting on the stove until both syrups reach 144.5°C.
Add 20 drops food coloring to one beaker.
Pour immediately. Pour colored liquid into inside beaker and
clear (or yellow) into outside beaker.
Candy will drip out on its own at first.
If cladding is not surrounding core on all sides, readjust funnels.
Use spoon to test viscosity. If you can pull long fibers, then the
viscosity is right for fiber drawing.
Pull the fibers, and save them on the metal tray.
Notice how rate of pulling affects thickness of fibers.
Notice how viscosity affects thickness of fibers.
Experience Fiber Drawing Success!
Video plays after download – brief wait
Procedure: Examination of Fiber
To view fibers under microscope, tape
three microscope slides together.
 Cut fiber with razor.
 Polish fiber by twisting one end on a damp
paper towel.
 Tape fiber vertically to the three slides.
 Position the three slides in the microscope
the way you would normally position a
single slide.

Acknowledgements
My Advisors: Dr. Bill Heffner and
Professor Himanshu Jain, Lehigh
University
 My Lab Partner: Raina Jain
 Funding Provided by: The National
Science Foundation through the
International Materials Institute, Lehigh
University
