Uncovering skeletons
used to mean very little could be done to determine
who the victim was and if appropriate, who the murderer
was. However, with growing technology and experience
of years, facial reconstruction now provides an answer
to such mysteries.
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Once the skin and flesh
has rotted away from the skull of a corpse, their character
and physical appearance disappear along with it. It
then becomes the job of forensic anthropologists,
sculptors and creative artists, to reconstruct a life
like form of what the person looked like from the skeleton
and sometimes, remaining parts of a skeleton. Clay is
a common form of reconstruction.
In
order to reconstruct a life-like face, sculptors
need to know the depth of skin that overlays the
skull. Sculptors usually begin sculpting with
20 to 35 tissue layers, scattered all over the
face. The main heavily concentrated depths are
situated around the mouth and in between the eyes.
Facial depth measurements are available for male
and female, certain ages, racial groups, thin
people and obese people. Small pegs are used as
facial depth indicators and are fixed into the
skull or otherwise into a cast of the skull. Strips
of clay that have been made to match the height
of the pegs are then placed between them and once
the strips are in place, clay is used to fill
the gaps between each peg.
*
The effectiveness of clay reconstruction depends
greatly on the skill of the sculptor. Photo courtesy
of Martin
Evison.
The
sculptor is then able to start work on the eyes,
mouth, ears, nose, chin, jaw and cheeks, as these
are the aspects of the face that give the most
character, but are also the parts that perish
most quickly as the body decays. Sculptors rely
on certain rules during the reconstruction of
a face, for example, the width of the nose is
the same as the distance between the inner corner
of the eyes and the corners of a person's mouth
lie below the inner boarders of the iris. Ears
are seen as being roughly the same length as the
nose, though elderly people usually have longer
ears. Once the facial features are complete, the
sculptor makes a mould from the clay head using
a plaster of Paris silicone rubber.
*
The facial features of a victim provide the most
infsormation on identity. Photo courtesy of www.imageafter.com.
Now, the reconstruction
of the face involves the task of building the muscles
around it. Sculptors must approximate the muscle structures
by noting the shape and size of certain facial bones,
as these will directly affect the shape of the muscles
previously attached to them. Using their experience,
the sculptors are able to build the face by shaping
each of the muscles and then fixing each one in its
place on the skull. The final step is to cover the clay
muscles with a layer of clay skin, which is smoothed
over so that it resembles real skin.
However experienced
the sculptor is, there are certain accuracy limits that
occur during the reconstruction of a face. Sculptors
can only guess hairstyles and cannot create the expressions
on a persons face that make the sculpture completely
life like. However, a sculpture is successful if it
aids in jogging someone's memory or can narrow down
a search by excluding anyone whose face does not resemble
the reconstructed face.
Computer facial reconstruction
has developed far enough to allow a virtual form of
reconstructing the face from a skull, making it easy
and efficient to travel from computer to computer. Such
software allows for a 3D image/structure of the finished
face to be rotated and moved around on a monitor.
Using computer facial
reconstruction does not require artistic skill, but
it does require skills of a different sort. There is
no standard method of computer facial reconstruction
but the initial data and facial shape comes from a 3D
scan of the skull. This process is non-destructive to
the skull and involves the skull rotating on a turning
table whilst a laser scanner lights up a thin perpendicular
strip. Mirrors located on either side of the turning
table reflect the images from the lit up area to sensors.
The data that the scan produces allows a controlling
program to determine the distances of each point located
on the skull. This then creates a digitalised model
of the skull that is easily and freely rotated on the
computer screen.
Applying
muscle and skin to the bone requires computer
tomography
(CT) scans of actual living people, which acquire
images showing where bones cast shadows onto the
skull and record hard/soft tissue (bones and flesh)
in a 3 dimensional, view. Using CT scans, data
files record the shape of the skull as well as
the tissue depth. Forensic anthropologist's knowledge
is also utilised in choosing an appropriate form
of CT scan. Any clothing found with the bones
can provide a clothing size, which is useful,
as it allows scientists to adjust any tissue depth
measurements to account for obesity or thinness.
Merging the two scans, the CT scan is applied
to the digital scan of the skull, becoming two
skulls on top of each other. At this stage of
the process, the two skulls are different shapes.
The computer program distorts the skulls' marks
on both so they match each other and at the same
time, distorting the facial tissue properties,
creating a facial shape that resembles the victim.
*
CT scans provide the latest technology in the
reconstruction of an unknown identity. Photo courtesy
of Martin
Evison.
CT scans cannot record
vital surface detail such as hair, skin and eye colour,
so these aspects of persons face must be added. This
involves borrowing the physical features of a living
person in order to paint these features onto the 3D
model. A person who has similar age, racial qualities,
and build as the modeled skull is used in a 3D rendering
process called 'colour mapping'. This process involves
photographing the face of the person with similar qualities
and using software to merge the three views into one
strip that is put onto the computer to complete the
reconstruction. The final result can be viewed and turned
on the screen. Like clay facial reconstruction, the
method does have its accuracy limitation. Nose, mouth
and ear shape are largely down to guessing, however,
lighting conditions and the ability to view the face
from any angle makes computer facial reconstruction
very lifelike and helpful during investigations.
