Current recycling practice includes glass separation by color before glass re-use because manufacturers use a cocktail of additives designed to change glass properties. The additives change the way the glass sets and the hue of the glass, while maintaining the structural integrity of the glass. For industrial process specifically, however, the change in the way glass sets is not necessary. Thus, the only reason for the cocktail of additives is to color the glass. The goal of this project was to examine how an increase in the Fe2O3 content of soda lime glass affects its strain resistance and color. Glass with Fe2O3 concentrations by weight of between 0.2% and 0.4% have comparable strength and hue with glass made using the standard cocktail of additives. Thus, Fe2O3 can be used in the place of the standard cocktail, solving the problem of glass separation in recycling.

1. Building
Better Bottles
- Nathaniel Mahowald -
Fe2O3 as an alternative to traditional glass colorants

2. Personal Information
I am a junior at
Mass Academy for
Math and Science
I started research
in glass in
September of 2013
All
experimentation
was performed at
my house

3. Purpose
The goal of this project was to examine how an increase
in the Fe2O3 content of soda lime glass affects its strain
resistance and color, because if Fe2O3 can be used as a
substitute to current additives, then it will save recyclers
money and open up new types of glass to be recycled.

4. Background Information
•Additives That Commonly Change Glass
In boro-silicate glass Fe2O3
Increases density
Increases the amount of green light absorbed by the glass
Hypothesized that increase in density is correlated to an
increase in strength
•Cr2O3, Mn2O3, Fe2O3, Ni2O3, Y2O3, Ce2O3, Nd2O3 and Er2O3
•Selenium and chromium oxide colorants;
Large amount of Se and Cr are used
•Defects are more common
•Each of these has unique and often unpredictable effects
•These colorants can be rare or expensive, especially ones with
rare earth metals
Powdered Fe2O3

5. Background Information
•Use of Multiple Additives Impair Single Stream Recycling
Limited amount of glass of colors and compositions other than the target composition can exist in the
batch before problems arise
More cullet = less energy taken by the glass recycling process
Energy costs drop 2-3% for every 10% cullet used
All shattered glass must be exempt from the typical recycling process because it cannot be sorted
The cost of sorting glass greatly increases the cost of glass recycling
•Use of a single additive would alleviate this problem
The cullet would melt to a homogenous mixture
Magnetic properties increased significantly (in boro-silicate glass)

6. Background Information
•Industrial Container Production differs in its Requirements from other Settings for Production
•Safety and color
Brand recognition purposes.
Glass retailers sell glass that has been treated so that it expands and contracts as it cools at the same rate as
the glass it will be molded with.
Use a slew of additives to augment this aspect of the glass, though the container manufacturers don’t
need it

7. Background Information
•Methods of Assessing Glass Strength
Use of fracture mechanics
Stress is defined as load over area, it is a key benchmark for
determining the strength of a solid
Strain is the change in length over the original length
Structures under stress carry “strain energy,” or the amount of
energy necessary to propagate a crack
A “test piece” is commonly used to generalize the material
properties of a substance
The two main indicators of load bearing ability are plane stress
and plane strain
The American Society for Testing and Materials has defined a
limiting thickness standard for these types of tests
A common method for
assessing the strength of
glass, called the drop
weight method

8. Background Information
•Methods for Hue Analysis of Glass
Open source software called Image J. allowed them to
quantify qualitative data collected using computer analysis of
their photos to identify patterns
Variables to control for in glass production
•Quality of the glass is essential
•Foreign Phases” cause major problems
•Inconsistent heating
•Mishandling of glass while it cools
•Allowing air to permeate the glass
•Homogenization of additives is essential
The Kiln that I used to
make my glass

9. Hypothesis
If the amount of Fe2O3 in soda lime glass
is increased, then the hue of the glass will
darken, and the strength of the glass will
remain constant.
If this hypothesis is confirmed, it would indicate Fe2O3 is a viable
alternative

10. Materials Required
1. Taylor Lithium brand scale
2. Metal pan of dimensions 30.8x39.6cm with a lip
3. 2 wooden planks of dimensions 64.9x2x15.4cm
4. Metal broom handle diameter 2.1cm length at least 25cm
5. 5 gallon water jug
6. 2 5 gallon home depot buckets (with lids)
7. Funnel small enough to fit the mouth of the jug
8. 1 liter measuring cup
9. Plastic container about 26.4x13.2x10cm
10. Towels
11. Ruler
12. Camera
13. Soda lime glass with incrementally increasing Fe2O3
content (between 0 (control) and 1 wt. %, at 0, .2, .4, .6, .8,
and 1) produced using 6 hour batching at 2,300 degrees
Fahrenheit and a cylindrical graphite mold of dimensions
2.54cm in height and 3.81cm in radius. (10 samples at each
concentration, as well as 10 samples from green bottles)

11. Obtaining the Glass
-The glass that used was batched in an
Econo-Kiln
-The batching period was 6 hours, at
2,300ºF
-Each sample contained 200g of Soda
Lime glass, samples of like composition
were batched together
-Batching started with a graphite
crucible, but that melted, so a steel one
was used in its place

12. Materials Analyzed
Iron (III) Oxide
Fe2O3
Soda Lime Glass
74 SiO2 · 13 Na2O · 10.5 CaO
1.3 Al2O3 · 0.3 K2O · 0.2 SO3
0.2 MgO · 0.04 Fe2O3 · 0.01 TiO2

13. Procedure
1. Take pictures of all samples in well lit environment against a white
background
2. Lay towel down on work surface
3. Place wooden planks parallel to each other 11cm apart on towels
4. Fill plastic container with water
5. Place sample perpendicular to the planks so that it rests on each and
crosses them
6. Place broom handle parallel to the planks such that it rests on the
sample
7. Place pan (lip up) centered on the broom handle
8. Place Funnel in the mouth of the water jug
9. Place jug (empty) on the pan
10. Use measuring cup to add water, pouring slowly
11. Pour until jug fills or samples break
If the jug fills, fill Home depot bucket with water in jug, place jug
on top of bucket and continue to fill
If the sample breaks, use scale to weight all that rested on top of it at
the point of breakage
12. Repeat steps 5-11 10 times and record masses
13. Repeat step 12 4 times, using each sample

14. Results
•P value after conducting an ANOVA of less
than .001. The strain capacity peaks when
the concentration of additive is at
.2, then drops
•The industry standard strength is not
outside of the range of standard deviation of
both the control and glass with .4% Fe2O3 by
weight.
Control is found not to be significantly
different from the industry sample, with a p
value of .62.
.4% concentration and the industrial
standard are significantly different (p value
of .013)
Essentially identical - industrial standard
glass was obtained from an industrially
approved container.
Glass with exclusively Fe2O3 is at least as
strong if not stronger than current glass
throughout the range between 0% and .
4% additive by weight

15. Results
•P value after conducting an
ANOVA of less than .001.
•Asymptotic increase in hue,
•Industry standard additives not
outside of the range of standard
deviation of .2% through .6% Fe2O3
by weight
•Industrial sample when compared
to the theoretical model posed in
figure 6 has a percentage difference
of 1.37%
Percentage of all shades of green
that can be safely achieved with
this additive: 57.87%

16. Results
A B
86
85
84
83
82
81
3631
X
Y
.4%
Fe2O3
Industry
Resistance
(kg)
This figure shows how similarly the .4%
Sample performed when compared to the
Industry Sample, showing that glass
with .4% Fe2O3 would be comparable
when it comes to strength

17. Results
This graph shows the
trend of color to
increase as the Fe2O3
increases, with .4%
Fe2O3 exactly in the
range of the industrial
sample

18. Assumptions
•Imperfections, bubbles, and impurities in the glass were assumed to be fairly
consistent
Low percentage relative standard deviation. The average percentage RSD was
3.223%, which constitutes high precision
•Another assumption was a consistent and high Young’s modulus for the glass
No bending was detected, and variations in the Young’s modulus were not reported
by other similar studies so it is unlikely that Fe2O3 changes the Young’s modulus in a
way that would compromise the results

19. Conclusion
The evidence supported the hypothesis that increasing the Fe2O3
concentration overall decreased glass strength and darkened hue,
specifically green hue. The goal of the project in attempting to find a
viable alternative to the cocktail of additives used by bulk glass
manufacturers was also supported. Now that glass can be made with
one additive only, it will no longer cause recycling problems and may
even become 100% reusable, returning to a pure stage between uses.

20. Future Applications/Extensions
•Between 0 and .4% Fe2O3 by weight, glass produced is at least as safe as glass found in manufacture
today
Included in that spread are the colors most likely to be used in industry.
A single additive could be used to augment the color of glass and in the process, solving the
problems of recycling.
The cullet could melt down to a homogenous mixture of two components
Magnetic properties could allow for 100% single stream recycling
•Identify the magnitude of propagation of magnetic properties specifically in soda lime glass,
•Design of the process by which the additive could be safely extracted, especially because as the Fe2O3
becomes separated from the molecular structure of the glass, it loses its magnetic properties
•Procedure for batching glass that has exclusively FeeO3, to find the most efficient method for its re-use.
Research about what the new tolerance for other types of glass in the batch becomes when only Fe2O3 is
desired
•Changing emission of UV radiation of glass with increasing levels of the additive