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The most stable of plastics used in photo preservation, polyester, does not generate any harmful chemical elements, but nor does it have any capability to absorb acids generated by the photograph itself.
Polyester sleeves and encapsulation have been praised for their ability to protect the photograph from humidity and environmental pollution, slowing the reaction between the item and the atmosphere.
This is true, however the polyester just as frequently traps these elements next to the material it is intended to protect.
This is especially risky in a storage environment that experiences drastic fluctuations in humidity or temperature, leading to ferrotyping, or sticking of the photograph to the plastic.
Photographs sleeved or encapsulated in polyester cannot be stored vertically in boxes because they will slide down next to each other within the box, bending and folding, nor can the archivist write directly onto the polyester to identify the photograph.
Therefore, it is necessary to either stack polyester protected photographs horizontally within a box, or bind them in a three ring binder.
Stacking the photos horizontally within a flat box will greatly reduce ease of access, and binders leave three sides of the photo exposed to the effects of light and do not support the photograph evenly on both sides, leading to slumping and bending within the binder.
The plastic used for enclosures has been manufactured to be as frictionless as possible to prevent scratching photos during insertion to the sleeves.
Unfortunately, the slippery nature of the enclosure generates a build-up of static electricity, which attracts dust and lint particles.
The static can attract the dust to the inside of the sleeve, as well, where it can scratch the photograph.
Likewise, these components that aid in insertion of the photo, referred to as slip agents, can break down and transfer from the plastic to the photograph, where they deposit as an oily film, attracting further lint and dust.
At this time, there is no test to evaluate the long-term effects of these components on photographs.
In addition, the plastic sleeves can develop kinks or creases in the surface, which will scratch away at the emulsion during handling.

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