BRONZE CARE

 Bronze can be maintained for years of use and enjoyment provided some basic care and attention is given to its preservation.  The first step in the care of bronze is to understand, minimize, or eliminate conditions that cause damage.  The second step is to follow basic guidelines for a maintenance program.

We try to provide some information useful in the care of bronze objects, but we encourage professional consultation if a serious condition exists.  American Bronze Fine Art Foundry, Inc. recommends you confer with an expert prior to any repair.  If you feel comfortable attempting a repair yourself, always test any procedure in an inconspicuous area first.  American Bronze Fine Art Foundry is not responsible for the failure or further damage created by the execution of the procedures outlined on this page.

IDENTIFYING BRONZE

Bronze is an alloy of copper. (Two or more metals are combined to form an alloy. Alloys generally have a different appearance or working properties from their component metals.)  Other alloys of copper include brass, "gunmetal," bell metal, and German silver also called Nickel silver.  Historically cast bronze is 90% copper, 6% tin and 4% zinc.  It has been widely used since antiquity for sculpture and decorative objects.

Bronze is traditionally patinated anywhere from light green to dark brown.  Patinas are sometimes described as any controlled corrosion that imparts an aesthetically pleasing color and/or texture.  Patinas may be applied with chemicals and paints or may have accumulated over time naturally; in any case, owners should be aware of the potential value of these finishes.  (The confusing part may come in differentiating pale green patina from potentially harmful corrosion; this will be addressed below).

Brass is an alloy of about 70% copper with about 30% zinc. It may be cast into solid shapes, rolled into thin sheets, spun into vessel shapes or drawn wire.  Many decorative objects, housewares, furniture hardware and inlays, and tools are made of or contain brass.

A third category should be included in any discussion of bronze and brass, that is "bronzed" and plated finishes. Sometimes called "French Bronze" in the Nineteenth century, paint or varnish containing bronze pigments were applied to cast iron or soft white metal.  These painted finishes may develop copper oxidation, but should not be polished.  Another method of bronzing involved applying a very thin copper plating to a metal surface; this kind of finish does not hold up to polishing either.  Please consult a conservation professional before attempting to treat these unique statues.

CAUSES OF DAMAGE

Corrosion, poor handling and inappropriate storage are the major causes of damage to statues.  Copper alloys are relatively stable, corrosion resistant materials if they are properly cared for.  Active or "problem" corrosion causes a loss of metal from the object, and is caused by inappropriate storage or a display environment which is heavily polluted, or subjected to evaporating salt water.   Mishandling, however, can result in a serious loss of value if denting, breakage, bending or cracking occurs.  Salts, oils and moisture can cause corrosion to develop, "staining" copper alloys, so if you handle uncoated statues with bare hands you risk damaging them.

CORROSION

SAFE CORROSION
Uncoated copper alloy statues kept clean and dry will usually maintain stable surfaces.  Stable surfaces may appear reddish, black to brown, or green to blue.  The brownish and black colors may result from natural, nondestructive oxidation of the copper, which is sometimes misnamed "tarnish."  Thick crusts may accumulate, but some corrosions which do not progress may actually protect the object if they are left intact (the green on the Statue of Liberty for example).  Purposely applied, "patinas," which may be any variety of colors usually act as a protection to the metal.

PROBLEM CORROSION
Active corrosion: If you notice the development of small spots of light green powder that grow rapidly, your bronze may be suffering from what is commonly called "bronze disease."  As mentioned, green surfaces are often seen but may not be cause for alarm if the corrosion layer is continuous and does not flake off easily.  Bright or "waxy" whitish green powder forming in small areas on the surface, or in cavities on the metal surface indicate advanced active corrosion.  If left untreated, this type of corrosion can cause a significant amount of damage to copper alloys, as it causes pitting of the surface and a continuous loss of metal. This condition is sometimes noticed when green powder falls from an undisturbed object.  It is caused by the presence of salts in the air, or by deposits left behind from inappropriate cleaning or handling and progresses when the air is humid.  High levels of ammonia pollution in the air will cause bluish deposits of corrosion.

Dust and grime left to accumulate on statues will actually hold moisture to the surface, and may induce corrosion.  Varnished or lacquered bronze and brass can usually withstand corrosion as long as the coating is not broken.  Where there are losses in the coating, corrosion will progress, usually seen as dark streaking where unprotected areas have oxidized.

ABRASION, DENTING
Objects with thin walls or fine ornamental detailing can be damaged by rough handling.  Raised areas and handles are especially susceptible to denting and joint failure. (See Handling, below).  If brassware is being used in the home, their owners should accept a certain amount of wear and tear from handling and more frequent cleaning and polishing.  Repairs to valuable statues, may involve braising or raising and reshaping dents should be done by a qualified expert.

CARING FOR YOUR BRONZE AND BRASS

Since statues made in part or entirely from copper alloys are so varied, it is not possible to cover all aspects of treatment in this document.  Your first line of defense will be good storage and/or maintenance.

HANDLING
Bare bronze should not be handled with bare hands.  Salts and oils from your skin can etch into uncoated metals and may even cause permanent damage.  Fingerprints are often discernible as darkened disfiguring marks on uncoated areas.  Soft cotton gloves or any clean glove or rag may be employed for this purpose.

Lift objects from their center of gravity, and avoid lifting objects by lip, limbs, handles, spouts or other extended areas; the metal may have developed unseen weaknesses over time and may bend or break unexpectedly.

Most home environments are safe, but generally speaking, basements are damp and therefore should not be used for storage.  Do not allow dust to accumulate on stored objects.  You may choose to drape plastic or cloth curtains around storage shelves, but do not place statues in sealed plastic bags; the danger of moisture condensation on the metal outweighs the benefit of dust protection.

CLEANING AND POLISHING
If you choose to attempt cleaning your bronze or brass, and you are sure of the surface appearance you wish to achieve, some of the following suggestions may help:

Cleaning
Stable or painted surfaces should be kept dust free. Vacuum clean all stable statues regularly, using the nozzle attachment with a brush.  A bristle brush, or a toothbrush may help to raise dust from crevices.

Sometimes surface grime can be removed satisfactorily with soap and water. We recommend a plain soap in a 3% solution in water. Use deionized or distilled water, and rinsing is a very important step.  If the dirt you want to remove is very greasy, "Vulpex" may be used in mineral spirits, in a 3% solution; rinse with straight mineral spirits.  It is especially important to remove old polish residues, which appear usually as dark green, gray or white deposits in cracks.

Calcareous (lime or hard water) deposits may respond to a 10 % solution of regular "Calgon" (sodium hexametaphosphate) in distilled or deionized water.  Allow the solution to soak into the crust and then remove by scrubbing with stiff brushes.  Then rinse thoroughly in distilled water.

Degreasing
The presence of degraded oils and grime may promote corrosion.  You can degrease most uncoated statues with mineral spirits. (Please consult the manufacturer or Material Safety Data Sheet for complete safety requirements.)  Wipe it over the surface in a small, inconspicuous area first to test for discoloration.  After the solvent has evaporated, check for any undesirable effects (usually caused by residual dust or an old finish).  Continue the cleaning process, using mineral spirits- dampened cloths to lift the grime.  You may find that sharpened bamboo skewers, nylon bristle "parts brushes", craft stencil brushes or even tooth brushes help you to get into crevices and joined areas.  If straight mineral spirits does not seem to be raising the grime, a surfactant, "Vulpex", may be used in a 1% solution in mineral spirits.  Be very certain to rinse with clean mineral spirits to remove residual detergent.  This method is Not recommended for old copper with richly patinated surface accumulations.

Corrosion removal
Very heavily corroded objects, like those unearthed or found in water, statues with original painted surfaces or those damaged by salts may require the assistance of a trained expert.  By attempting to remove thick corrosion with steel wool or other scrapers, you may end up scratching or abrading the metal surface.

Polishing
Some bronze may have been polished to a bright finish, and altering original surfaces may reduce the historical value of an object.  As mentioned above, some dark, stable surfaces may be considered "patinas."  Collectors should be aware of any special finishes, especially lacquers and patinas, which may determine the correct color the metal should be, the degree to which it should be cleaned and/or the degree to which it should be polished.  If you come across any special coating after you have cleaned off the simple dirt, you may wish to consult with an expert before proceeding.

If you wish to return a bronze or brass object to its original, polished appearance, it is usually possible with a fair amount of elbow grease and a good polishing compound.

Old lacquers must be removed prior to polishing.  If the lacquer is original and in fairly good shape, you may consider investing in a professional treatment to preserve it.  Lacquer removal is best done with acetone, preferably by immersion.  Acetone is a volatile solvent that should never be used in a poorly ventilated area. (Please consult the manufacturer or Material Safety Data Sheet for complete safety requirements.)

Polishing with a mild abrasive is the only safe cleaning method recommend.  Copper and its alloys are relatively soft metals.  Commercially available "dips" may contain undesirable components such as hydrochloric or sulfuric acid which act too quickly and remove more metal than simple polishing does.

Some commercial paste polishes are quite abrasive and may scratch your fine metalwork.  For statues not suffering from heavy corrosion "Duraglit Wadding" polish may be somewhat less abrasive than others.  Light polishing may be done using jeweler's cloth containing rouge ( i.e. "Birk Cloth", "Hagerty Glove").  A museum-proven, safe polishing method is as follows:

POLISHING METHOD 1
For most polishing use fine calcium carbonate, CHALK, ("whiting") worked into a slurry or runny paste with equal amounts of ethanol (denatured alcohol, ethyl alcohol) and distilled water.  The paste is rubbed across the surface, working a small area at a time, with cotton balls or clean cotton rags.  Detailed areas may be polished with Q-tips in the paste or with cotton wadding on the end of a sharpened bamboo skewer.  Depending on the design of your object, it may not be desirable to over-clean every crevice, as this decreases the overall contrast of the detailing.  It is important to remove all residual polish with distilled water.  Drying may be accelerated by adding ethanol to the rinse water, or by giving the object a final wipe with ethanol.

POLISHING METHOD 2
Some statues may not respond to the special treatment outlined above because the oxidation layers are too thick.  For an admittedly more abrasive method, use "Solvol Autosol" for general purpose polishing.  Test for the degree of polish you wish to achieve on a small inconspicuous part of the object.  Buff on the polish with a clean rag.  The surface must be rinsed with mineral spirits after polishing to remove any polish residues.  This polish can be recommended because it contains less ammonia than other commercial brands.  Ammonia can cause long term damage to valuable bronze objects.

COATING

Polishing exposes fresh, reactive metal to the atmosphere and, therefore, to further oxidation.  You may wish to coat objects that will not be used.  We lacquer valuable silver and brass for their protection.  This also eliminates the need for frequent polishing - a process that inevitably wears away the metal surface if done frequently.

Wax

For most collectible bronze and brass statues, the best coating we can generally recommend is wax.  Wax provides a relatively flexible coating that is easily applied and that can be renewed.  It can be used on top of original patinas and lacquers that you do not wish to disturb, as long as they are cleaned first.  Use "Renaissance" wax, or other "microcrystalline" waxes in most cases, because it is inert and will not yellow over time.  It is applied to a degreased surface with a clean cloth, and buffed out with a rag or bristle brushes (shoe polish brushes are great for this purpose).

For better adhesion, you may wish to dilute the wax in mineral spirits or varsol, brush it on, let the solvent evaporate and then buff with a rag or soft shoe polishing brush.  An alternative, on objects made entirely of metal, is to gently and briefly heat the degreased surface with a hair dryer before applying the wax. (Do not try this if heat sensitive materials such as wood and ivory are nearby.)

Again, wax is not an appropriate coating for all metal surfaces, especially where it is impossible to cover the whole object, or where the slightly glossy finish would be inappropriate.

Lacquers

Lacquering involves the use of solvents to clean the metal properly (acetone or tri-chloroethane).  On large areas of metal a spray-applied lacquer achieves the most even and durable finish.  Spray lacquering is a task best left to qualified individuals with the training and equipment necessary to do a good job.  Poorly applied lacquers can actually cause more severe corrosion if small areas are left exposed.

If there are small areas or pieces of a bronze that need coating, you may achieve satisfactory results by brushing on a lacquer.  We recommend "Incralac" lacquer, which is formulated for use on copper and copper alloys.  It is soluble in the solvents xylene and toluene and must be used in a well-ventilated area. (Please request a Material Safety Data Sheet and instructions when you order this product).  The metal must first be scrupulously clean, and you should always wear gloves to handle the artifact after it has been polished.  Just prior to applying the lacquer, the artifact should be given a final degreasing with acetone.  Lacquer gives a shiny luster to the metal.