Light effects

Yasmin Jayathirtha

In the last column, (Teacher Plus, August 2013) we looked at reactions that have been used for millennia and continue to be used, almost unchanged. This month we will consider a set of reactions that were observed about 150 years ago, gained popularity rapidly and suddenly, over the last 20 years or so, just died out, replaced by a newer technology. I am talking about reactions caused by light, which gave us photography, blueprints, ammonia prints, all of which have now been superseded by other technologies.

The abbreviated timeline for the history of photography is as follows:

1727 – Accidental discovery of the photosensitivity of silver salts by J Schulz
1800 – Sun pictures using leather soaked in silver salts by Thomas Wedgwood
1826 – First permanent image by Nicephore Niepce
1837 – Louis Dagurre made the process of making pictures public
1850 onwards – Boom of studio pictures with plates
1889 – Kodak camera with roll film released
1900 – Kodak Brownie box camera with roll film released
1900 onwards – lots of pictures taken by lots of people
1991 – digital technology comes to the fore
2004 – Kodak ceases production of film cameras

Lots of people are still taking lots of pictures but now they are being uploaded online or kept on discs. The use of film has virtually ceased.

Blue prints and diazo ammonia prints were developed so that plan drawings could be copied easily after draftsmen had made the first master drawing. These have now been overtaken by scanners and photocopying.

The author works with Centre for Learning, Bengaluru. She can be reached at

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