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Transparent Storage .

Transparent Storage

Plastic enclosures for conservation storage.

Because of their transparency plastics are commonly used for the protection of archival documents and photographs. However many of the first plastics used were later found to be harmful to the objects they enclosed. The most common plastic used was PVC (polyvinyl chloride). It has good transparency and can be welded with ease. The problem was that it contained a large amount of plasticiser to keep it flexible. In time this plasticiser comes to the surface and transfers a sticky acidic residue to the enclosed object. Plasticisers are not the only danger from poor quality plastics. Polypropylene is often recycled and can have fatty acid slip coatings to make it run smoother on production machinery.

Polypropylene, Polyethylene and Complex Plastics

Only virgin Polypropylene without this slip coating should be used for photographs or archival material. Virgin Polyethylene, without plasticisers or harmful additives that might off-gas, is suitable for archival storage but it lacks rigidity and clarity. When applied as a thin film to Polyester it gains strength and rigidity but the crystal like transparency is reduced. The recent inclusion of reactive copper and carbon particles in plastics now offers new possibilities for the long term protection of archival material. This is also the case with multi layer oxygen and moisture barrier films which combined with the use of vacuum or oxygen scavengers can greatly slow down the rate of deterioration of a variety of sensitive materials.

Polyester

Polyester is known as the most stable and chemically inert plastic used for conservation storage. It offers optical clarity, strength, rigidity and a surface free of slip coatings.

Melinex® and Mylar® are the most commonly known brands of Polyester. The clarity, purity and resistance to degradation is prized by conservators, however it is much harder to weld and form into pockets and complex album pages than softer plastics such as Polyethylene and Polypropylene which have a lower melting temperature. Polyester can be welded with heat but the temperature melt band is very narrow, meaning, too much heat and it will crystallise, too little and it will not weld.

Ultra Sonic welding is the most effective technology for welding the edges of a pocket. Timecare® ‘Crystal’ Album Pages can be made using this process. Ultra sonic welders and spot welders are listed in the equipment section of this catalogue. Timecare® ‘Crystal’ Polyester storage pockets/enclosures are edge welded using a ‘Bead’ welding process similar to that of the ‘Original Curateur™’ polyester welder machine supplied by Conservation By Design.

The Timecare® Polyester HCL Album Pages developed for the popular Timecare® ringbinder boxes utilise a combination of the strength and durability of polyester with the ease of welding of polyethylene. Album pages made solely from polyethylene or polypropylene, although cheaper in material and production costs, do not offer the same level of strength or protection against fire in a disaster scenario.

The same multi layer technology employed by the HCL album pages is used for the oxygen and moisture barrier films and pouches listed in this catalogue. These products allow visible storage in a controlled atmosphere with the absence of oxygen achieved by gas flushing or oxygen scavengers using nanotechnology.

Heavy weight matt polypropylene is an excellent material for making large drawer files. The matt surface is non reflective and has reduced surface contact with the contents. It can be welded or sewn as with our Visifile™ folders. In use it makes an almost indestructible folder that allows the contents to be seen at a glance.

Controlling the atmosphere or environment is crucial for good storage of all kinds of material, but photographs are particularly sensitive to humidity. A stable relative humidity (RH) should be sought to avoid fluctuations that can cause cracking of surface coatings. Photographs generally require around 40% RH and 55% RH is recommended for other paper based items. If the RH exceeds 65% and it fluctuates there is a danger of ‘Ferrotyping’ or adhesion of the photographic surface to the plastic enclosure caused by condensation.

For the professional archive, Conservation By Design offer an integrated temperature and humidity ‘room within a room’ system which is modular and can be tailored to the size of the space available, no matter how big. For the smaller user, De-humidifiers, ProSorb™ and Silica Gel are available and although they are no substitute for a well controlled environment good quality acid free boxes offer a low cost ‘buffer’ against fluctuations in temperature and humidity.



Categories

Polyester & Polypropylene Storage
Polyester & Polypropylene Storage
Storage and Transportation Bags
Storage and Transportation Bags
Oxygen and Moisture-Barrier Bags and Films
Oxygen and Moisture-Barrier Bags and Films

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