Photography with slow emulsions

Captured on glass Part 2

Dual mugshot of woman seated and standing, with standing shot showing blurred movement.

Ada McGuinness (alias Edith Mitchell, Edith Cavanagh), Special Photograph number D33, 26 July 1929, Central Police Station, Sydney (detail to show movement). New South Wales Police Forensic Photography Archive, Sydney Living Museums

Many of the Special photographs show evidence of long exposures where sitters have moved during the exposure time, causing a blur in the final image.

This is probably in part due to the slow emulsions on the dry plates used to produce these photographs.

Dual mugshot of woman seated and standing, with standing shot showing blurred movement.
Ada McGuinness (alias Edith Mitchell, Edith Cavanagh), Special Photograph number D33, 26 July 1929, Central Police Station, Sydney New South Wales Police Forensic Photography Archive, Sydney Living Museums
Dual black and white mugshot, man seated, and man standing with hat on.
William Stanley Moore, Special Photograph number 1399, 1 May 1925, Central Police Station, Sydney. New South Wales Police Forensic Photography Archive, Sydney Living Museums
Half of dual mugshot showing blurred face of seated man with head being held by pair of hands.
Bing Chong, Special Photograph number D66, 31 May 1928, Central Police Station, Sydney. New South Wales Police Forensic Photography Archive, Sydney Living Museums

The part of the negative that holds the photographic image is called the emulsion. The emulsion has a number of components that includes a light sensitive compound – commonly silver. The emulsion is exposed to light in the camera.The emulsion sensitivity is the starting point for determining an accurate exposure.The exposure is worked out using the sensitivity of the emulsion (expressed today as an ISO value), the amount of light passing through the lens (controlled by the aperture) and the amount of time the lens is open (controlled by the shutter speed). The slower the emulsion, the greater the amount of light and/or time required to correctly expose the negative.

Controlling the light falling on the scene in front of the camera is near impossible when photographing with sunlight. The photographer needs to choose the best combination of shutter speed and aperture for a correct exposure based on the available light level.

Although it was the middle of a gloriously sunny day in summer using handmade dry plates in a workshop at Gold Street Studios in Trentham, Victoria, my exposures were more than a second and I was unable to remain motionless, so I appear blurry in the final photographs. The relatively slow exposure times were due to the liquid light emulsion we used to create the dry plates. This emulsion is about 3 ISO according to workshop notes. This is very slow especially compared to modern silver gelatin film emulsions (usually from 100 ISO), or the split-second exposures taken by sensors inside digital cameras.

Black and white photo of woman in garden.
Photograph in the style of the Specials, standing in positive. Photo Holly Schulte © Sydney Living Museums
Black and white photo of woman sitting on chair in garden.
Photograph in the style of the Specials, seated in positive. Photo Holly Schulte © Sydney Living Museums

At about 6 ISO, the dry plates used by Sydney Police in the 1920s were a similar light sensitivity to the liquid emulsion.

The slow emulsion helps to explain the long exposures required when photographing with available light in the holding yard at Central Police Station, and also explains why some of the subjects appear unsharp or blurry in the photographs.


Find out more about our upcoming 1920s Mugshots Photography Workshop with Holly and photographer Enrico Scotece:


 

About the author

Portrait of woman against background of prickly pear foliage.

Holly Schulte

Curator Digital Assets

Holly is the Curator Digital Assets with Sydney Living Museums where she is part of the Collections & Access team.