Silvering out is caused by chemical breakdown of the silver used to form the image in 19th and 20th century photographs. The silver reacts with atmospheric contaminants such as hydrogen sulphide and peroxides leaving a bluish or green tarnish in the darker areas of the photo....
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| Scan by Carterworks showing silvering |
Sulphiding is where this reaction causes the photo to change from black to brown and create overall fading.
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| Scan by Carterworks showing sulphiding |
Over time these chemical reactions lead to a loss of photographic information or unsightly distortions and marks on the image. Luckily both these images were captured in time and have been restored by Carterworks.
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| Restoration by Carterworks |
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| Restoration by Carterworks |
The National Gallery of Australia recommends that photos should be displayed away from direct light, ideally behind UV glass and in temperatures of around 21 C and with a relative humidity of 50%. They also recommend that photos
be mounted and framed or interleaved and stored with archival quality chemically stable acid-free plastics such as polyethylene, polypropylene or polyester. Archival paper products should be neutral pH, unbuffered and lignin, sulphur and peroxide free. One sure way to determine if something is archival quality is to check if the material passes the American National Standards Institute Photographic Activity Test (ANSIPAT) .
Source:http://nga.gov.au/conservation/prevention/photos.cfm
In NZ you can get these archival storage materials for your photos and documents from:-
Conservation Supplies (online and in Havelock North) http://www.conservationsupplies.co.nz/
Port Nicholson Packaging in Wellington http://www.pnp.co.nz/archival-storage/
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