12.3: Footwear impressions
- Page ID
- 53153
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)As previously mentioned, a footwear impression is very useful to any criminal investigation. To understand footwear impressions, it is first necessary to understand how shoes are made and the nomenclature that is given to the manufacturing of shoes.
Modern athletic shoes are divided into three basic components:
- The upper
- The mid-sole
- The outsole
The Upper
The upper may be constructed from leather, synthetic leather, suede, mesh, polyester, nylon, or a lightweight high-performance textile called Flyknit. The upper holds the foot securely over the midsole platform while providing flexibility and support.
The Midsole
The midsole platform gives the foot a stable cushion. The midsole can be made with lightweight foam called ethylene-vinyl acetate foam (EVA), pylon, or polyurethane.
The Outsole
The outsole is the bottom of the shoe. It provides durability and traction on a surface. The outsole can be made with a solid durable rubber compound, a carbon rubber compound, a blown rubber compound, a durable rubber material that contains 10% recycled rubber, or ethylene-vinyl acetate foam.
Outsole manufacturing processes
- Die cutting process
- Outsole cutting process
- Injection mold process
- Open pour mold process
- Ethel vinyl acetate
The modern outsole manufacturing processes the forensic technician will most likely encounter are the die cutting, open pour mold, and ethel vinyl acetate processes.
The die cutting process has been around since the 1940’s and remains popular in Nike Cortez™ tennis shoes. Like a cookie cutter, the die is pressed onto a sheet of pre-formed rubber, and a design is “cut” for the outsole. Where this process is unique is in the way the cutter hits the sheet of rubber in a different a location each time; therefore, the “chevrons” of the pattern are never the same length.
The open mold process is used by companies like Vibram™ (Quabaug) to produce outsoles for work and hiking boots. The outsole is poured, hardened, and then glued or nailed to the mid-sole.
Although EVA is the most common method of outsole manufacturing, the calendar press mold process can still be found in some countries and in boutique or handcrafted footwear manufacturers. The calendar press mold process involved rolling sheets of warm rubber is fed through a series of heated rollers that press the rubber into a thin, uniform, and durable sheet of rubber from which the patterned outsoles are cut. The outsoles are then glued onto the midsoles of the shoe.
Other Shoe Terminology
Below is a pictorial list of other useful shoe terminologies:
