Most North American horse bells made in the last two centuries are brass. Some may have been cast from bronze or other alloys, but these bells are the exception, not the rule.
Brass is any alloy -- mixture of metals -- that contains mostly copper, with zinc as the second largest ingredient. (1) Other elements such as lead, iron, phosphorus, nickel, or tin may also be present in small amounts. The amount of any ingredient can vary widely, however, depending on factors such as cost, working properties, color, intended function, etc.
Most older bells have a warm red-gold color when polished, while new bells typically have a distinctive yellow-gold color. This is due to the different amounts of copper in the alloys used -- an alloy with more copper has a more reddish color.
Older bells may be made of red brass or semi-red brass that contain 75 to 90% copper. The balance of these alloys is mostly zinc, tin, and lead. Some modern red brass alloys include (2,3,11):
Leaded Semi-Red Brass Alloy C84400: 81% copper, 9% zinc, 7% lead, 3% tin.
Red Brass Alloy 230: 85% copper, 15% zinc
Red Brass Alloy C83400: 90% copper, 10% zinc
Newer bells are usually made of a yellow brass alloy with a much higher zinc content such as (2,3,11):
Cartridge Brass, Alloy 260: 70% copper, 30% zinc
Yellow Brass, Alloy 270: 65% copper, 35% zinc.
Tombac (tombak or tambac), known also as German or Dutch Brass, is a brass alloy that contains about 84% copper. (9) Tombac may be similar or identical to Red Brass alloy.
German Brass should not be confused with German Silver, also known as Nickel Silver, Tutenag (India) and Paktong (China), and by many proprietary tradenames. (12) Although it is silvery white when polished, Nickel Silver contains no real silver -- it is any alloy of copper, zinc, and nickel. One type of Nickel Silver is Alloy 752, which contains about 64% copper, 17% zinc, 18% nickel, and a trace of manganese. (2,3) Nickel Silver is often used as a substrate for electroplating. Plated items with a Nickel Silver base may be labeled EPNS: electroplated nickel silver. (12)
Bronze, as defined in centuries past, is any alloy that is mostly copper with tin as the second largest component. (1) Small amounts of other elements such as lead, phosphorus, zinc, iron, or manganese may also be present.
Today, the term bronze is also used for copper alloys that contain little or no tin. Examples include aluminum bronze, manganese bronze, and beryllium bronze. (1) Copper-tin alloys are often called "tin bronzes" to more correctly identify them.
Bell bronze is an alloy used for large open mouth bells, because it has unusual acoustic properties. It is a blend of 20-25% tin and 75-80% copper with small amounts of lead and other metals. The alloy composition of older bells varies, however, from bell to bell and even within a particular bell. The metallic composition of the venerable U.S. Liberty Bell varies widely. This may have weakened the bell and contributed to its famous crack. (10)
A commercially available tin-bronze Alloy C91300 may be comparable to bell bronze. This alloy has about 80% copper, 19% tin, and 1% trace metals. (11)
Some copper-zinc alloys called bronzes are probably more correctly called brasses. These alloys contain very high percentages of copper. They include Commercial Bronze, Alloy 220, about 90% copper and 10% zinc, and Jewelry Bronze, Alloy 226, about 88% copper and 12% zinc. (1,2,3)
Color. New, well-polished "yellow" brass bells typically have a bright yellow-gold color. Brass can appear reddish, however, if the zinc has been removed from the surface metal by improper cleaning with harsh acids. Brass can also look red or pinkish if it is a "red" brass alloy.
Bronze can look exactly like yellow brass or it may look almost like copper. The color depends on the amount of surface oxidation and the kind of bronze alloy used.
Both brass and bronze can appear silvery if the item has been plated with a silvery metal such as nickel or chrome. Obviously, color is not a reliable way to decide if your bell is brass, bronze, or some other metal.
Magnetic properties. Bronze and brass are both fairly heavy, nonmagnetic metals. If the bell is attracted to a magnet, it definitely not brass or bronze. It is probably mild steel or iron instead. If your bell is non-magnetic, but very light, it is probably aluminum, zinc, or other lightweight metal.
Sound test. The sound test is probably the best way to distinguish bronze from brass and other non-magnetic metals -- short of a full chemical analysis -- but it takes careful experience to accurately identify bronze from other metals by sound.
Lightly tap the outside of the bell with a pencil, coin, or other small, hard item. Bronze will have a clear, loud, silvery sound that has a distinctive ringing quality. The sound should persist for several seconds before dying off to a fainter tone and then to silence. Brass and other metals have a softer, duller tone that dies off more quickly.
Chemical properties. The only positive way to identify the metals in an alloy with chemical tests such as spectrographic analysis. Unfortunately, this is not a practical or affordable way for most people to determine whether a horse bell is brass, bronze, or other alloy.
Plating is the process of putting a thin layer of metal onto an object by a chemical reaction, by a mechanical process, or by using an electrical current. Gold and silver were the first metals used for plating.
Mechanical plating. Gold was mechanically plated onto silver as early as the mid 1200s when Bartholommeus Anglicus warned that the presence of dust, moisture and wind would prevent gold plate from bonding properly to its silver base object. (8) Vermeil or fire-gilded objects were made as early as the 1500s by the dangerous process of amalgamating (dissolving) gold in liquid mercury. The gold amalgam was then bonded onto silver. The mercury was removed by heating the plated object until the mercury evaporated. (6,8)
In the early 1700s, silver was plated onto objects in several ways. Sheets of silver were fused onto a heated metal object with hammer blows (French plating) or by fastening the sheets onto the object with tin solder ("close" plating). The original Sheffield silverplate made from 1743 through the late 1800s was created by fusing a thin layer of molten sterling silver onto a copper underlayer. (6)
Chemical plating. The main process for chemical plating in the 1700s and 1800s was "water gilding" in which a very thin "flash" layer of gold was chemically bonded to inexpensive objects. (7)
Electroplating. An Italian researcher first used an electrical current in the early 1800s to plate precious metals onto objects. (7) The process was not used commercially until the late 1830s or early 40s, when brothers Henry Elkington and George Richards Elkington of Birmingham, England first patented their process for electroplating gold and silver. Within 10 to 15 years, commercial processors offering gold and silver electroplating were found throughout Europe and North America. (6,7)
Silver- and gold-plated horse bells were offered by some manufacturers in the 1800s, although it is my impression that these bells are fairly unusual, especially the gold-plated ones. Electroplating became commercially available in North America in the 1850, so it is reasonable to assume silver- and gold-plated horse bells were produced in the 1850s and later.
The plating on many vintage horse bells -- whether silver, tin, nickel, gold or chrome -- has often worn away from use, polishing, and time until only traces of the original plating remain.
The art of mechanically plating tin onto other metals, iron in particular, had been practiced for centuries, but the industry became widespread in Europe only after 1730. (13)
Nickel plating was first developed in the 1840s by the German scientist Böettger who noted that the plating "...because of [its] slight oxidablity, great hardness and elegant appearance [was] capable of many applications." (4) The first U.S. patents related to nickel plating processes were granted in 1869 and 1878. (5)
It is very common for the plating on sleigh bells to have been mostly or completely worn off from use. In our experience, only bells dating to the late 1800s show any evidence of plating. Cleaning these tin- or nickel-plated bells requires a light touch to preserve the soft plating.
Plating with chrome was developed much later than nickel plating. The information I have found so far suggests the process was first commercially available in North American in the early to mid 1920s.
There are several types of chrome plating that result in different surface finishes. I am not well enough informed about this subject to be able to say what type of plating was used on horse bells. Regardless, bells that were chromed were originally as bright and silvery as the bumper on a show car. The chrome plating on the bells we see today, however, is almost always damaged and dull from use and time.
Those of us who are not plating experts could probably confuse "bright nickel" plating with chrome plating. I tell the difference by the surface texture. Nickel plating tends to wear off evenly, so the surface of the bells feels smooth to the touch. Chrome plating tends to flake or peel off, causing the surface of the bells to feel pitted and rough.
References
1. Metals Dictionary. Metal Mart. Source: http://www.metal-mart.com/Dictionary/dictletb.htm
2. Alloy Information. National Bronze and Metals, Inc., Houston, Texas. Source: http://www.nbm-houston.com/
3. Alloy Information. Radcliffe Wire. Source: http://www.radcliffwire.com/alloy_copper.htm
4. History of Plating - The Early Years. New Brunswick Plating, New Brunswick, New Jersey. Source: http://nbplating.com/
5. Beverly A. Graves. Nickel Plating Primer. Products Finishing magazine. 1 April 2002. Source: http://www.pfonline.com/articles/040102.html
6. Gary Kirsner. A brief history of beer steins. Beer Stein Library. Beer Steins America, Inc. Source: http://www.beerstein.net/articles/bsj-4e.htm
7. A short history of electroplating. Metal Arts Specialties, Leonard, Michigan. Source: http://www.artisanplating.com/articles/platinghistory.html
8. Alan W. Cramb, Ph.D. A Short History of Metals. Dept of Materials Science and Engineering. Carnegie Mellon University, Pittsburgh, Pennsylvania. Source: http://neon.mems.cmu.edu/cramb/Processing/history.html
9. Webster's Revised Unabridged Dictionary. 1913 edition. Source: http://dict.die.net/
10. Bronze. Liberty Bell Memorial Museum, Melbourne, Florida. Original location of website: http://home.att.net/~tom.jordan/LibertyBell/history/bronze.htm
11. Copper Alloy Database: North American Cast Copper Alloys. Anchor Bronze & Metals, Inc., Cleveland, Ohio. Source: http://www.anchorbronze.com/alloydatabase.htm
12. Richard Mervyn Leveridge. Nickel Silver, German Silver and related alloys. Jewellery and Silver Society of Oxford (JASSO), Abingdon, Oxfordshire, England. Source: http://pages.zoom.co.uk/leveridge/nickel1.html
13. George Randall Lewis. The stannaries: a study of the English tin miner. Houghton Mifflin and Co., Boston. 1908. pp 57-58. Source: Google Books, http://books.google.com/books?id=3fBCAAAAIAAJ&source=gbs_navlinks_s
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