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Microfilm that is not Brown Toned is susceptible to destructive Redox, a condition that, if left unchecked, will result in partial or total data loss.
Because of the intrinsically volatile nature of silver (think of how fast a tea service will tarnish) it makes a great medium for capturing photographic images on film. However, even though this residual silver has been "fixed"
it is still susceptible to degradation over decades through oxidation and exposure to various atmospheric gases.
However, there is a superior method for producing microfilm, that converts this volatile metallic silver into a very stable silver sulphide*. This is called polysulphide toning, or Brown Toning.
Only Heritage Microfilm Brown Tones each and every roll of master microfilm we produce, ensuring true 500 year life expectancy (LE).
The Brown Toning process requires that a processor have 4 more tanks than other deep tank processors. The extra tanks allow for two tanks to be committed to Brown Toning and two more to a thorough rinse of the film after Brown
Toning. The process will usually require the processor to be set up to manage different temperatures for the developing process and the Brown Toning process to ensure correct post brown toning density and conversion to silver
sulfide.
Brown Toning is the first line of defense against microfilm deterioration. In addition, Heritage uses molecular sieves and regular inspections to ensure against irreplaceable data loss. For those who have advanced microfilm
damage, Heritage offers specialty restorative microfilm duplication.
Proper Brown Toning requires a very special processor setup and careful replenishment of a volatile brown tone mixture to assure accurate conversion. We believe any lab that does not perform daily monitoring of silver sulfide
conversion may well not be achieving any significant protection of their microfilm images.
Heritage is the only commercial lab that Brown Tones every roll of silver microfilm we produce. When you choose Heritage, you ensure that your historic publication will be preserved for generations far into the future.
* According to the Image Permanence Institute (IPI) at Rochester, NY, silver sulphide is factors of ten more stable. |
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