2017 Gerald R. Ford Conservation Center
About Brass & Bron ze
Objects composed of brass or bronze roded do not accurately reflect the ap- are commonly found in the home, in pearance originally intended by the the form of vessels, plates, plaques, artist. The care procedures described weapons, and ornaments. Both brass in this handout are for historic and and bronze are known as “copper al- decorative arts objects that have been loys” because they are both made of determined to be stable. They are not copper which has been alloyed with appropriate for ethnographic or ar- other metals to achieve different work- cheological materials. ing or visual properties. Brass is com- posed of copper alloyed primarily with zinc, while bronze is composed of cop- per alloyed with tin. As they age, the alloying constituents and manufactur- ing processes affect the way these ma- terials deteriorate. Objects that have been damaged, mishandled, or cor-
Han dl in g Inside this issue: Because copper and its alloys are so Always support the object with two
Handling 1 reactive, contact with the salts, oils, hands while handling. Avoid holding and acids on human skin can lead to it by an appendage such as a handle. Cleaning 3 etched and/or corroded surfaces. To
Waxing 5 prevent continued damage, wear cot- ton, latex, or nitrile gloves when han- Storage and Display 6 dling artifacts made from these materi- als. Remove all jewelry that could Consulting a Conserva- 7 tor scratch the object while you are han- dling it. Make sure that you have a Additional Resources 7 clean, dry place to examine the object
before you move it. Caring for Brass & Bronze
Examine the structure carefully, look- tection from corrosion. Decorative ing for cracks, weak areas, old repairs, paint is easy to detect on the surface, and loose or missing parts. Once you but transparent organic coatings, like have thoroughly examined the struc- shellac, are sometimes hard to see. If tural condition, consider the surface of the coating is peeling or lifting from the object and whether it is safe for the surface, it may be visible with a you to clean yourself. bright light and a strong magnifying When examining the surface it is im- glass. Transparent coatings were em- portant to determine what, if anything, ployed both to prevent surface oxida- is on the surface. Intentionally applied tion and to provide a golden appear- ance. Removal of original paint or a organic coatings, such as paint or shel- lac, were often applied to enhance an transparent coating would perma- object’s appearance and provide pro- nently diminish the object.
Patina
Another important type of decorative created in a number of colors, but and protective surface often applied to shades of brown, gray, black, or blue/ copper alloy objects is patina. A patina green are predominant. Patinated sur- is a thin, chemically-induced layer of faces are sometimes enhanced and relatively stable corrosion on the sur- further protected with a thin coat of face of an object. While patinas can clear or pigmented wax. It is impor- form naturally over time, they are of- tant to avoid removing an intentionally ten intentionally created as a part of applied patina. the finishing process. Patinas can be
Corrosion Products
Sometimes copper alloy objects are disfigured with spotty, uneven, or blotchy blue/green corrosion products. These corrosion products cannot be easily reduced or removed in a mu- seum, historic house, or home setting. If your object has this problem, or if you are uncertain about its appearance Page 2 or features, consult a conservator for guidance on proper care. C l eanin g
If the artifact is structurally sound, it has ingredi- no evidence of original organic (such as ents Materials to Have on Hand shellac or paint) or inorganic surface such as Clean towels and clean white sheets to create a coatings (such as a patina or plating), vinegar, padded workplace. and has only minor superficial soil and/ baking Cotton swabs or pads, as or tarnish, proceed with caution. Mate- soda, needed rials and techniques used should be ex- and Gloves: nitrile (these gloves offer the best tremely gentle to avoid causing unnec- lemon protection when working essary deterioration. juice with mineral spirits and wax. Latex gloves do not Avoid the use of commercial polishes, should offer adequate protection.) since many contain corrosive chemicals be avoided, Mild detergent such as such as ammonia or harsh abrasives that clear, unscented, can permanently damage delicate sur- as these dishwashing liquid faces. They often also contain corrosion substances can damage copper al- Distilled water (1 gallon – loy surfaces. The materials and half of this should be inhibitors that, while useful on house- reserved for rinsing) techniques listed below have been hold items that are currently in use, can Large container for dilute tested by conservators and found detergent solution (such cause unusual or tenacious re-corrosion as a 5 gallon bucket) to be safe and effective when used in a display setting. Instructions using Soft, clean, natural bristle with care. brushes, such as haké, watch, or paint brushes
Cleaning Procedure Apron or smock to protect clothing
Prepare a clean, well-ventilated work Use thin sheets of clear polyethyl- Mineral spirits (if needed) area for the cleaning process including ene plastic sheet to mask out any Clear microcrystalline adequate light and sufficient ventilation nonmetallic elements such as paste wax, such as Renaissance© wax, or a to remove solvent vapors. A clean wooden handles to protect them clear paste wax such as towel covered by a clean white sheet during cleaning. Behlens® paste wax. can be used to create a padded work Clean natural bristle stencil brushes, or shoe surface on your table. Wear protective buffing brushes, for nitrile gloves to avoid contaminating waxing and buffing both the object and your hands. Wear Polyethylene plastic sheet a clean cotton smock or apron to pro- tect your clothing. To the extent possi- ble, disassemble the artifact. Take digi- tal images and notes to be certain that Page 3 parts can be reassembled correctly. Caring for Brass & Bronze
Remove any loose dirt or dust by cilitate removal. Gently agitate with a dusting lightly with a soft brush. Haké soft brush to help loosen embedded brushes are good choices for dusting material, and then rinse thoroughly because they are made entirely of with clean cotton swabs dampened in wood or bamboo. If a soft artist’s distilled water. Remove any waxy or brush is used, cover the metal ferrule oily accretions by moistening a cotton with tape to avoid scratching the arti- pad or a wad of loose cotton with min- fact. Do not use dusting cloths as eral spirits and wiping the surface. If they will not reach into small crevices, wax is trapped in candle cups or depres- and can scratch objects if trapped grit sions, saturate a small wad of cotton is rubbed over surfaces. Be careful with mineral spirits and place it on the not to scratch the surface of your ob- wax for a short period to soften. Once ject. the wax is soft, push it off with the Small copper alloy objects sometimes blunt end of a bamboo skewer and re- have iron wires rolled into the rims or move any residue with cotton damp- edges to increase their structural ri- ened with clean mineral spirits. Avoid gidity. Do not wet these areas with scratching the surface with old polish water under any circumstance. Do and accumulated grime by using the not allow liquids to penetrate hollow lightest functional working pressure. handles or other hollow parts that are Change swabs often to reduce risk and use a rolling rather than rubbing mo- difficult to rinse or dry. Never im- merse the object in a bath of water. tion. Make sure your work space is well -ventilated if you use mineral spirits. Old polish residues trapped in re- cessed areas are a common problem found when cleaning historic copper alloy objects. Many commercial pol- ishes contain waxy components that cause the abrasives to stick to the sur- face. These can usually be removed by applying a few drops of dilute de- tergent solution (made by mixing a squirt - approximately a teaspoon - of clear, unscented dishwashing liquid in about a half gallon of water) with a In many cases, the cleaning actions soft brush or cotton swabs. A short listed above will be enough to remove Page 4 amount of waiting time may help fa- light tarnish and fingerprints from the surface. Because many copper alloy WARNING: When working objects are not meant to be bright with solvents, always follow all recommended safety precau- and shiny, it is best to avoid polishing tions noted on the containers. them. Wipe the object gently with Mineral spirits are flammable pieces of clean flannel or loose cot- and their fumes can be harmful ton, changing them frequently to pre- to your health if not used with vent surface abrasion. Allow the ob- care. Nitrile gloves should be used during the cleaning and ject to dry completely in a warm, dust waxing procedures, as they free environment. offer protection from mineral spirits and the solvents present in the wax mixture. Always be aware of the location of the nearest fire extinguisher when Waxing working with flammable sol- vents and waxes. To protect the object from water and dence of discoloration. The wax airborne pollutants, apply a small should provide good protection for amount of microcrystalline paste wax at least a year, if the object is kept in to a soft, clean, dry cloth or very soft stable environmental conditions. If brush and rub it over the entire sur- the item must be handled, wear face of the object, being careful to get clean cotton or nitrile gloves. For complete coverage. Do not apply too objects on permanent display, con- much wax; only a small amount is sider having a conservator profes- needed. Wait a moment and buff the sionally clean the object and apply a wax out with clean pieces of old silk, stable organic resin coating. This du- clean old nylon stockings, or soft rable and protective coating can pro- brushes. Wax has a flat plate-like vide up to twenty years of protection structure and buffing helps align and and minimizes the wear and tear as- compress the plates for a more com- sociated with repeated handling and plete and protective coating. If you dusting accidentally leave unbuffed wax on the surface too long, apply a small amount of fresh wax to soften the dried wax and buff immediately. To maintain the wax coating, periodi- cally dust the object with a soft natu- ral bristle brush and check for evi- Page 5 Caring for Brass & Bronze
Storage and Display
For maximum protection, keep metal Avoid using containers or shelving com- objects indoors, in a space other than posed of wood, which can off-gas harm- a garage or damp basement. Store ful acidic vapors. Materials such as them at least four inches above the wool, felt, and rubber, should not be floor to prevent water damage from stored with the object as they can emit floods or leaks. If possible, house the sulfur gases. objects in a closed container to pre- Copper alloy objects should be stored vent dust accumulation, which can so they do not touch other metal ob- attract moisture to the object’s sur- jects, or lay directly on a metal shelf. face, resulting in corrosion. Closed Either of these situations can lead to storage also minimizes the object’s corrosion. Sheets of acid-free tissue pa- exposure to atmospheric pollutants per, thin polyethylene foam, or clean, and changes in relative humidity. undyed cotton can be used as a barrier Polyethylene or polypropylene stor- between metal surfaces or as suppor- age tubs are readily available and can tive padding underneath an object. be identified by the “PE” or “PP” im- print found on their underside. An- other storage option is boxes com- posed of acid-free, lignin free board.
Environmental Conditions
Copper alloy objects are best pre- It is also important to protect objects served by keeping them in a clean, from overexposure to light, which stable environment, where the tem- causes irreversible damage, especially perature is kept below 72°F and the to organic materials and coatings. Ex- relative humidity is kept between 30 posure can be partially limited by using and 50%. Higher humidity levels will window shades and applying UV filter- result in corrosion on metal surfaces. ing films to windows, and sleeves to If there are organic materials such as fluorescent lights. Remember: light ex- wood present with the metal, keep posure is cumulative and the surest way the relative humidity above 40% to to protect your object is to keep it out keep the organic components from of direct light (both natural and artifi- drying out. cial) and limit the amount of time it is Page 6 on display. Consulting a Conservator
If your copper alloy object is unstable, damaged, or exhibits original paint, coatings, or applied patina on the surface, it is best to have it looked at by a conservator before trying to clean and wax it yourself. A conserva- tor will be able to assess all the issues relating to its care, and determine an appropriate treatment that does not diminish its value. Conservators can provide basic structural repairs, corrosion reduction, protective coatings, and proper storage materials for objects.
Additional Resources
Canadian Conservation Institute. Care of Metals. Retrieved from http://canada.pch.gc.ca/ eng/1453994182990 American Institute for Conservation of Historic & Artistic Works. Caring for Your Treasures: Metal Objects. Retrieved from www.conservation-us.org/docs/default-source/resource-center/paintings.pdf
Conservation Suppliers
Conservation Resources International Light Impressions 5532 Port Royal Road 100 Carlson Road Springfield, VA 22151 Rochester, NY 14610 Toll free: (800) 634-6932 Toll Free: (800) 975-6429 www.conservationresources.com www.lightimpressionsdirect.com Archival housing/storage supplies, photographic supplies, general Photographic supplies, housing, matting and framing supplies
Gaylord Archival University Products P. O. Box 4901 517 Main Street Syracuse, NY 13221-4901 P. O. Box 101 Toll Free: (800) 448-6160 Holyoke, MA 01041 www.gaylord.com Toll Free: (800) 628-1912 General conservation supplies, housing supplies www.universityproducts.com General conservation supplies, housing and matting supplies Hollinger Metal Edge, Inc. 6340 Bandini Blvd Talas Commerce, CA 90040 330 Morgan Ave Toll Free: (800)-862-2228 Brooklyn, NY 11211 www.hollingermetaledge.com Telephone: (212) 219-0770 Archival housing/storage supplies www.talasonline.com Conservation supplies, photographic supplies, general
This project was made possible in part by the Gerald R. Ford Conservation Center Institute of Museum and Library Services grant 1326 S 32 Street Omaha, NE 68105 LG- 43- 12- 0 4 6 3 - 1 2 . www.imls.gov 402-595-1180 [email protected]