Have you ever thought about how
images appear on photographic film?
How can light capture
images on a piece of paper?
It is a very simple process.
Light causes the formation of durable
chemical compounds,
which after being exposed to certain
conditions reveal an image.
The development process in photography
consists of using silver chloride.
But nothing stops us from using other
chemical reactions triggered by light.
One of the most well-known reactions
of this type is photosynthesis:
the basic process used by all
green plants on Earth.
Plants use chlorophyll to capture
electromagnetic energy,
which than serves as a reduction
agent for converting CO2 into sugar.
From this a plant produces a polysaccharide
energy store also known as starch.
Starch is stored in leaves
and other parts of plants such as tubers.
To check the starch content, we use an iodine
solution that dyes the starch dark blue.
This can be used to develop
a photograph on the leaf.
Starch will replace the silver that
darkens photographic film.
Dyeing the starch is the equivalent
of the film development process.
For my experiment I am going to use a
popular plant with plain leafs: Tropaeolum.
This plant was hidden
in a box for two days.
Without light, photosynthesis didn’t occur
and no starch formed in the leaves.
Starch that was already stored in the leaves
was used for cellular respiration.
I am fixing a negative of the image
I'd like to develop onto the leaf.
The next step is to leave it
in sunlight for a few hours,
which is what I have already
done with this leaf.
Photosynthesis occurred here, but only
in the places that weren't covered.
The leaf has gathered starch.
Our task now is to expose it
and develop the image.
I start by removing the
air from the inside
of the leaf by putting
it in hot water.
Next I need to remove the chlorophyll
to prevent its green colour from
darkening the image.
Hot alcohol is excellent for this task.
Then I wash the leaf in water
and place it in an iodine solution
to develop the starch pattern.
After a few seconds we can see an image
appear on the surface of the leaf
that matches the photographic
negative we attached to it.
Photography and photosynthesis seem
like two very different things,
yet they both have features
ideal for the same thing:
capturing an image on a piece of matter.
