Basics Cci Lab Questions And Answers Pdf
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It includes 4 open-ended questions, and 20 scored items grouped into 4 parts. At the end, the material will get a final score and explanation.
Most metals corrode: iron rusts, copper turns green, silver turns black, and lead disintegrates into a white powder. Stored improperly, most of the metals in a museum collection will slowly transform into oxides, sulphides, carbonates, or other compounds. The corrosion processes are faster on metal surfaces contaminated by salts, volatile organic acids such as those from wooden storage cabinets , ammonia from cleaning fluids, or dust.
The rate of corrosion can also be increased through galvanic corrosion, a process that occurs when objects made of different metals are in contact with each other in high relative humidity RH conditions. For more detailed information, Selwyn For best protection of metal artifacts, museum storage areas must be clean and well-organized, have controlled RH , and have as clean air as possible.
This Note describes general guidelines for the proper storage of metals. It explains the role of RH , recommends general storage conditions and handling procedures, and discusses a few specific metals: aluminum, copper, iron, lead, plated objects, and silver.
For more detailed information, Drayman-Weisser Relative humidity is a key factor in metal corrosion because most metals corrode more quickly in moist conditions. For ideal storage of metals, the RH should be as low as possible. However, this is rarely practical, especially for mixed collections.
It is reasonable to store stable metal artifacts — that is, metals that do not exhibit signs of active corrosion — with the rest of the collection in controlled storage conditions. The drier conditions will reduce the corrosion rate, but the source of the corrosion will still need to be addressed.
Seek advice from a qualified conservator on the care and treatment of such objects. Small, important pieces can be stored in desiccators containing silica gel that has been dried completely or conditioned to a low RH.
Large numbers of unstable metal objects can be stored together in a small room or in a cabinet where RH can be kept low with a dehumidifier. Small silica gel dehumidifiers are suitable for this purpose.
Lithium chloride dehumidifiers are not recommended because of the risk of contaminating artifacts with lithium chloride, which could make the corrosion worse. For information on a low-cost unit for controlling RH , Michalski Humidity control systems require regular maintenance.
Empty the water pans of dehumidifers often, and check and recondition silica gel regularly. Although not necessary, it can be useful to store artifacts composed of similar metals together. This makes examination and retrieval easy and systematic. If objects such as silver trophies, medals, coins, tools, etc. However, the final decision on organizing storage depends on the collection and should be made by curatorial staff.
Whether storing metal artifacts in a separate room or with the main collection, select an area situated away from windows, doors, vents, and heating units. If windows cannot be avoided, ensure that they are tightly sealed to prevent leaks and condensation. The storage area should have sufficient air circulation to maintain an even temperature and humidity and to prevent build-up of corrosive gases, such as volatile acidic or alkaline vapours.
It is almost impossible to eliminate volatile substances from a museum collection. However, local high concentrations that will damage metal can be prevented if the room is adequately ventilated. Fans in the storage area will help to maintain airflow. Dust that settles on metal retains moisture. In urban areas, dust may contain pollutants, such as sulphur compounds, that tarnish silver.
Any chlorides absorbed in the dust on metal objects will accelerate the corrosion of the metal. Storage areas should, therefore, be kept clean and dust-free. Seal concrete walls and floors to reduce dust levels. Using chemically stable materials e. Although expensive, metal storage cabinets and shelves with powder coatings are ideal.
Other safe materials include polyethylene or clear food-grade polystyrene boxes, and acid-free unbuffered papers. Avoid wood and wood-pulp products because they release sulphur compounds and organic acid vapours acetic and formic acid. Also avoid oil-based and alkyd paints because they release volatile materials for long periods. Rooms that have been freshly painted with oil or alkyd paints should be aired for at least four months before metals are stored in them.
If there is doubt regarding the suitability of a material, contact Client Services at CCI for advice. Ideally, metal objects should be stored in closed systems, such as cabinets with well-sealed doors or drawers. Closed systems will protect metals from dust, pollutants, and, to a degree, changes in RH.
Dry silica gel can be placed in the drawers to maintain a low RH ; the silica gel should be checked and reconditioned regularly. One hazard associated with closed storage is the tendency for volatile materials to build up slowly over time. To prevent this problem, choose storage systems made of inert materials, such as metal. If open shelving is to be used for storing metals, the objects must be protected from dust and pollutants.
Wrap artifacts in acid-free unbuffered paper or place them in acid-free boxes or in polyethylene bags. As a further precaution, polyethylene or washed cotton dust covers can be draped over shelving units.
Never place metal objects directly on a storage shelf or drawer. Line shelves and drawers with closed-cell polyethylene foam such as Ethafoam, PolyPlank, Volara, Plastazote, or Nalgene. The foam lining also helps to protect the objects from shock or abrasion. Avoid urethane foams because they degrade easily. Arrange each metal artifact on a shelf or in a drawer so that its weight is evenly supported and so that it can be retrieved without damaging neighbouring artifacts.
For metals housed in drawers, place wads of acid-free unbuffered paper or strips of polyethylene foam between the individual objects to keep artifacts from moving when drawers are opened or closed.
Alternatively, individual supports for metal artifacts can be carved from thick polyethylene foam CCI Schlichting Metal objects can also be stored in clear plastic food-grade polystyrene boxes, polyolefin freezer containers e. Tupperware , or polyethylene bags. Boxes and bags may need to be perforated to prevent the build-up of condensation on the inside in the event that the storage area is not well controlled for fluctuations in RH. Polyethylene bags can be punctured several times with a small sharp awl or punch although this will leave rough plastic projections on the inside of the bag that could catch on the artifact.
Alternatively, the bag can be slit along the side with very small diagonal cuts. All holes must be small enough to prevent the artifact from falling out of the bag. Soft polyolefin boxes can be drilled through the sides beneath the handles. Avoid Saran Wrap because it contains poly vinylidene chloride. This slowly degrades to form hydrogen chloride HCl gas, which can damage metals. For an excellent source of ideas and practical solutions to storage problems, Rose and de Torres When removing metals from storage, ensure that they are supported well.
Transport fragile pieces in padded trays, boxes, or the artifact's own storage support. Wear well-fitting plastic or clean cotton gloves when handling metals. Cotton gloves absorb sweat and accumulate salts during use, so be sure to clean them regularly. Highly polished metals, such as silver and copper, are particularly sensitive to the oils and salts in skin. Avoid handling silver with latex rubber gloves because the sulphur compounds from the rubber may tarnish the silver over the long term.
Also, many pure metals and some alloys are soft and are therefore easily scratched or dented. Aluminum resists corrosion because of the protective oxide layer that forms rapidly when aluminum is exposed to air.
Normally, if the oxide layer is damaged by an abrasive action like scratching, it re-forms rapidly. Chloride ions prevent the oxide from re-forming and so cause pitting of the aluminum surface.
Following the guidelines in this Note will help to prevent the accumulation of surface contaminants that lead to this problem. Copper alloys are susceptible to corrosion by ammonia, acids, strong alkalis, chlorides, and sulphide gases.
It is best to store small copper artifacts in clear plastic boxes padded with acid-free unbuffered paper, or in boxes made from acid-free or neutral board. Larger artifacts can be wrapped in acid-free unbuffered paper, stored in carved Ethafoam supports, or placed on foam shelf-liners. Bronze disease is a form of active corrosion that affects archaeological copper alloys.
It is characterized by the eruption of a light-green powder in spots over the surface. Objects displaying bronze disease should be stored separately to keep the corrosion products away from other artifacts. Many of the general storage methods discussed here are not practical for large iron artifacts. Their storage is often dictated more by the availability of space than by environmental considerations. However, maintaining a clean storage environment and providing adequate storage supports for these artifacts contribute to their long-term preservation.
Stable lead surfaces are generally dark grey, while actively corroding lead is usually covered with a loosely adherent white powder. Lead is particularly difficult to store safely because it is easily corroded by very small amounts of volatile organic acids, such as acetic or formic acid. These acids can act rapidly, destroying surface detail and weakening the object. Formaldehyde, a source of formic acid, is released from the adhesives used in certain plywoods and particle boards.
Inspect lead objects regularly for active corrosion because lead is particularly susceptible to damage in poorly ventilated areas. If an object is actively corroding, isolate it and store it at a low RH. At the same time, identify and, if possible, remove the corrosion source often wood, paint, or adhesives or provide better storage conditions. To protect lead artifacts from harmful acids, wrap the objects with neutral and acid-free materials and store them in suitable containers.
Envelopes made for the archival storage of coins are suitable for small lead objects or fragments. Polyethylene and food-grade polystyrene boxes are also safe for lead.
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