SQ - Redford Cemetery "White Bronze" EarthCache

History

Centuries before zinc was discovered in the metallic form, its ores were used for making brass, and zinc compounds were used for healing wounds and sore eyes. Brass was produced by the Romans in the time of Augustus (20 B.C. - 14 A.D.). By 1374, zinc was recognized in India as a new metal and at Zawar, India, both zinc metal and zinc oxide were produced from the 12th to the 16th century. From India, zinc manufacture moved to China in the 17th century. Zinc was recognized as a separate metal in Europe in 1546. In 1743, the first European zinc smelter was established at Bristol in the United Kingdom.

Zinc Ores

Metal ores are generally oxides, sulfides, silicates, or "native" metals that are not commonly concentrated in the Earths crust, or "noble" metals. The ores must be processed to extract the metals of interest from the waste rock and from the ore minerals. Ore bodies are formed by a variety of geological processes. The process of ore formation is called ore genesis.

Ores containing zinc are widespread geologically and geographically and many ore bodies are still awaiting development when sufficient demand occurs. Ore veins are vertical to near vertical mineralized zones. They can be thinner than one inch or as wide as fifty feet. They are usually associated with “mineral districts” – multi-county areas with the widespread injection of minerals from deep within the Earths crust.

Usually zinc ores are found in association with those of lead, copper, gold, silver as well as other metals. Rarely is the ore, as mined, rich enough to be used directly by smelters; it needs to be concentrated. Typically zinc ores contain 3% to more than 10% zinc and zinc concentrates will contain 55% zinc.

Among several mineral ores,(ie: smithsonite, hemimorphite, zincite, & wurtzite), a mineral called sphalerite is the chief ore of zinc. It consists largely of zinc sulfide in crystalline form but almost always contains some iron. When iron content is high it is an opaque black variety,  marmatite. It is usually found in association with galena, pyrite, and other sulfides along with calcite, dolomite, and fluorite. Sphalerite is found in hydrothermal sulfide ore veins of any rock class, sedimentary, igneous, or metamorphic.

Mining

The Red Dog Mine, in Alaska, is the world's largest single producer of zinc and has the world's largest zinc reserves. Red Dog Mine accounts for 10% of the world's zinc production. It supplies 75% of the total United States production.The ores are hosted in black shales of the Kuna formation of Carboniferous age. The ore deposit is classically described as Sedex or shale-hosted base metal deposit.

Zinc ores are being mined in more than 50 countries with Australia, Canada, China, Peru and the U.S.A. being the leading producers. Owing to the nature of the ore veins, most zinc mines are underground but some newer mines are of the open pit type. In terms of production volume, open pit mines account for as much as 15% with underground mines producing 64%. 21% of mine production comes from the combination of underground and open pit mining.

Production

The raw material used for the production of zinc is zinc concentrate, which is the result of a flotation process after the ore has been mined and milled. The zinc ore contains 1-15% zinc whereas the concentrate typically contains approx. 55% zinc, 6.5% iron and 32% sulfur together with other elements at much lower levels.

The process begins with the roasting of the concentrate. At a temperature of around 950°C, oxidization of the zinc, iron and sulfur occurs. The iron and zinc oxides that, after the roasting process, have been reduced to powder form, are leached with dilute sulphuric acid. The solution is neutralized and the precipitates, i.e. metallic co-products together with any unwanted contaminants, are removed by filtration.

The refined solution is then electrolyzed in a cell fitted with a lead anode and an aluminum cathode. The cathode is immersed in the solution for 48 hours during which time the zinc is deposited on the aluminum cathode from which it is subsequently stripped.

The final process takes place in the foundry where the zinc takes its final form, either as a metal with a purity of 99.95% or as an alloy together with copper, aluminum or magnesium. The zinc is cast into various forms (normally ingots or plates)with weights from 9 kg to 4 tons.

Major uses:

Zinc is the fourth most widely used metal after iron, aluminum, and copper. Zincs major use is for corrosion protection coatings on steel (galvanized metal); as die castings, as an alloying metal added to countless other metals, as chemical compounds in rubber, ceramics, paints, and agriculture, and in pharmaceuticals & cosmetics. It's also a necessary element for proper growth and development of humans, animals, and plants.

Note: Todays U.S. one cent coin is 97.5% zinc, with the remaining metal being the copper plating.

  



 

A Historic use:

" White Bronze"

   The Monumental Bronze Company in Bridgeport began manufacturing the white bronze grave monuments in the 1870's. In the 1880's, the company opened subsidiaries, including Detroit Bronze, American Bronze in Chicago, and the Western White Bronze Company in Des Moines. There were also subsidiaries in Philadelphia and New Orleans. Some sources say that all the casting was done in Bridgeport, and the monuments were sent to subsidiaries for fusing. Other sources maintain that accounts are not clear as to whether casting was done at the subsidiary plants. The company ceased production of white bronze grave monuments in 1912 (or 1914). It is possible to find white bronze monuments with later death dates. The company continued to make inscription plates after it stopped production of complete monuments. Plates might be added to previously existing monuments.

 

  Hollow metal markers with a bluish-grey color, white bronze gravemarkers are actually cast zinc. They were manufactured by the Monumental Bronze Company of Bridgeport, Connecticut. White Bronze monuments were seldom sold locally, but were ordered by catalog through one of the company's sales agents. Company catalogs featured ads at the back encouraging people to become sales agents with "No capital investment needed." The catalog would list the various monument shapes, decorative markings, and panels which could be used. After the customer chose the overall design, the monument was cast in Bridgeport and then shipped to the customer's locale. Wax models were created, then these were used to make plaster molds for casting the zinc. A monument might be made of two or four separate panels fused together, depending on shape. All were hollow inside. Smaller inscription plates containing the individual's name, dates, or other information were bolted on separately with screws. Unfortunately, these are often damaged - plates may be removed, or the zinc screws replaced with steel screws, which can cause discoloration.

  The removable plates, revealing the monuments' hollow construction, gave rise to several folk beliefs about the monuments - that cemetery caretakers stored their rakes and garden tools inside them, that outlaws and robbers stashed their loot in the monuments, even that smugglers hid their liquor inside the monuments during prohibition. The fact that the monuments were catalog orders led some people to believe that Sears & Roebuck sold the monuments, but this was not the case. Because these monuments are rarely found, some people believed that a white bronze monument in a cemetery was a "display" or "demonstration" model put up by the monument company, but there is no evidence for this.

  Aside from the problems of plate removal, the white bronze monuments are usually very well preserved. Zinc resists corrosion, and exposure to the elements has formed a protective layer of zinc carbonate, which gives the monuments their characteristic blue-grey color. Castings are typically still quite clear and sharp, and do not suffer from the weathering, mosses, and lichens that pose such a problem for their stone counterparts.

One weakness that has damaged these zinc monuments is caused by the pressure from their own weight. Zinc has a tendency to creep, or bend when it's exposed to pressure over time. This creeping action may also cause tiny cracks on some of the monuments. Obviously, smaller markers do not exhibit this problem. Proper seating/mounting on concrete bases was important to reduce creep & corrosion from prolonged contact with the soils.

"Creep"....outward bending of base