The history of chemical photography

Today, with a digital camera, we can snap an image, upload it on the net and share it with our friend in a jiffy. But when photography started, it took hours to take a photograph, which would come out very blurred. Let’s take a trip backward in time, and see how photography began.

Photographs today
The physics of photography has never changed, ever since Mo Zi of China discovered it nearly 2400 years ago. He called it the ‘locked treasure box’. Light is let in through a tiny hole in the box (‘camera’ is the Latin word for room), where it falls on the opposite wall. There an image appears, of the thing being photographed. However, it depends on chemistry to actually record the image.

In a digital camera the image is recorded on a ‘camera sensor’ that has thousands of light-detectors which capture the amount and colour of light. Your photo is actually stored as an electronic code, which is decoded by your computer. Hardly chemistry at all.

How mom and dad took photographs
When a photo was taken, light reacted with silver iodide, causing it to break down into silver and iodine. Silver would deposit as dark spots on the film. Darker areas formed where more light fell, and vice versa. Depending on the layer, you’d have a silver spot matching the colour to which the layer was sensitive. This was called a ‘colour negative’ (they just called it a negative). Ask mom or dad; they might still have a few negatives from the old times.

Once photography was done, the ‘negative’ would be given to a ‘studio’ to process. In the studio, the technician would first put it in a ‘developer’ solution. The developer was a chemical called CD-4, which did two things. It made the conversion of silver iodide to silver go faster. It also reacted with the dyes, making them stick to the film along with the silver.

The negative was then converted to a ‘positive’. In this the negative was put in front of a light source, and projected onto photographic paper. (This is not very different from how a slide projector works). The photographic paper had light-sensitive dyes coated on it. When the photo was developed, it was washed and dried and finally ready to be given back to the customer. This was called the C-41 process. In those days, photos would take weeks before you could share them with friends, and photography was an expensive hobby.

How grandma and granddad took photographs
Life was simpler in their times, and also colourless. The nitrocellulose film used was coated with a single layer of silver iodide. When the photo was taken, it would come out in black and white. The negative was the exact opposite, dark in areas of more light and light where there was more light. Ask your grandma to show you negatives of their photos. You’ll see pretty weird images, in which pretty people might look quite ugly, the sun is a black disc and night looks like bright day!

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