Gold is a unique metal. It is valued not just for its rarity, but also for its range of lovely colors, the distinctive character of its soft metallic glow, its resistance to tarnish, and its easy workability. Gold is so soft and malleable that one-ounce can be stretched into a wire 50 miles long, or hammered into a sheet so thin it covers 100 square feet.
its pure form, gold is a shiny yellow metal and is relatively inactive
chemically. The chemical symbol for gold, Au, is from its Latin name,
aurum. With a specific gravity of 19.4, it is also one of the heaviest of
the common metals more than twice as heavy as silver or lead. Because
gold is chemically inert, it resists oxidation and other changes which
diminish the brilliance of other metals.
Countless ancient artifacts attest to golds popularity and versatility. The most malleable and ductile of all metals, gold has invited the highest skills of artisans and craftsmen all through the ages. For thousands of years gold has been wrought into articles of ornamentation, into religious icons and talismans, and, of course, shaped and formed into currency.
a symbol of beauty, nobility and constancy, gold has been cherished and
even worshiped Wars have been fought and nations conquered for gold. It is
because of its exceptionally high value that gold, in all its forms, from
the very beginning has required accountability, a system of weights and a
standardization of purity. It is not surprising that the need to assay and
account for gold led to the invention of the first scales and balances.
Legal regulations governing the marking of gold jewelry began in England as early as the year 1239. In that year, a law was enacted which established a procedure for authenticating the purity of the gold used in various articles of jewelry. The procedure involved the use of an official mark, which was stamped on the article at Goldsmiths Hall in London or at one of several British government assay offices. These "Hall marks" started a practice, which has since been duplicated in practically every civilized country of the world.
As noteworthy as the law was, perhaps equally noteworthy were the severe penalties and punishments inflicted against violators. For example, in 1397 two gold- smiths, convicted of using false stamps on their wares, were sentenced to have their ears nailed to the pillory in which they were to be placed. Similar retributions were exacted in most other countries for offenses of this type.
If the punishment for counterfeiting hallmarks seems severe, it should be pointed out that the laws were perceived as not only protecting the public against fraud, but also as the only safeguard the gold- smith trade had to maintain all- important public confidence in the quality markings on their products.
In the United States, Congress passed the National Gold and Silver
Marking Act to govern standards of purity of these metals for the
jewelry industry. This law also included standards of purity for gold
alloys. This practice required articles such as gold-filled and rolled
gold plate to conform to federally controlled standards.
The most recent amendment to the Gold and Silver Marking Act was passed in 1976. The key provision of this amendment tightened the purity tolerances of the gold or gold alloys in articles of merchandise, so that "...the actual fineness of such gold or alloy shall not be less by more than three one-thousandth parts than the fineness indicated by the mark stamped, branded, en- graved, or printed upon any part of such article." The amendment also requires the fineness of gold solders to be not less than seven one-thousandths less than the stipulated purity. The amendment significantly narrowed the "minus" tolerance of karat gold, which was previously set at ½ karat for gold articles and a full karat for soldered pieces.
The amendment also stipulated that the gold content of an article must be at least ten karats for it to be called "karat gold." It is worth noting that Handy &Harmans practice as a supplier assures the purchaser that his gold will be full karat gold. Handy k Harman assays every melt before the gold is shipped, to insure that there is no minus tolerance, and that the articles made from it will be full karat, not one part less than the karat stamped on them.
In the karat system, pure gold is expressed as "24 karats fine" (24K). (Pure gold in commercial practice is 99.95 to fine, but is nominally considered 100%.) The gold content of any gold article depends on the proportion of pure gold it contains. (See Chart B)
The most popular jewelry golds in the United States are:
24 K 100% gold (99.95 %)
18 K 18/24ths or 75% gold
14 K 14/24ths or 58.33% gold
10 K 10/24ths or 41.67% gold
Since any karat gold below 24K has other components, it is important that karat gold compositions be standardized and uniform. To achieve this objective, a concept known as "balanced karat golds" has been established.
Balanced karat golds are uniform alloys whose composition is consistent from batch to batch and from order to order. This consistency can be obtained only when the karat golds are made in quantity, under accurately controlled conditions of melting, pouring, rolling and heat-treating. The resulting consistency of surface finish, karat fidelity, accuracy of size and gauge and working properties simplify the manufacturers production operations and contribute to reducing the scrap factor.
One hundred-ounce bars of fine gold.
The metals that are combined with gold have a profound effect on its color, temper and hardness. The process of combining other metals (usually "base" metals) with gold is called "gold alloying," and the metals used in the process are usually called alloying elements. When the final compound contains more than 50% gold, the compound is usually referred to as a "gold alloy."
The most common alloying elements used in the United States are silver, copper, nickel and zinc. Each of these metals alters the color, tem- per, hardness and annealing characteristics of the gold. Although the metallurgical relationship between gold and its alloying elements is quite complex, in general the degree of change, which can be imparted to the gold, is related to the percentage of base metal used. The higher the percentage of base metal, the greater the change in the physical characteristics of the gold. Obviously, if identical amounts of the same base metal are added to equal weights of karat gold specimens, the base metal will have a more pronounced effect on the lower karat gold than on the higher karat gold.
Although experienced jewelers and goldsmiths know what special qualities they want and are familiar with the use of alloying elements to achieve them it may be useful to summarize how these alloying elements modify the various properties of gold.
Jewelry golds range from light yellow through deep yellow to reds and greens, and also include a family of whites.
Silver: As the proportion of silver increases, gold changes in hue from yellow to greenish-yellow, to white.
Copper: As copper content in- creases, the gold becomes redder in appearance.
Nickel: Nickel has the effect of whitening gold. The so-called "white golds" substitute nickel for silver.
Zinc: Zinc is considered a "decolorizer," and is used to convert some red golds (copper alloys) into a more yellowish tone by substitution of zinc for some of the copper and silver.
Pouring molten gold into molds.
Historically, the white golds were introduced to replace platinum. A typical alloy used was a 19%K gold, with about 81% gold, 16% nickel and 3 % zinc. At the lower karat levels, the added nickel made the alloy difficult to work. At 18K, some cop- per was essential for workability, with substantial amounts needed for 14 and 10 karat alloys. Because only small amounts of copper could be used in order to retain a white color, zinc was added as a softener, enhancing the whitening effect of nickel while reducing the need for red copper. The use of zinc, how- ever, was limited by its tendency to increase fire cracking the cracking that sometimes occurs around the grain boundaries of highly worked nickel-bearing white golds upon annealing. This is a fact well known in the industry, and is overcome by heavy, uniform working of the metal before annealing.
As weve noted, karat golds are made in red, yellow, green and white as standard colors. Shades of these colors are available as special compositions.
Even within a single color standard, however, the composition and the physical properties of the karat gold will vary considerably. In yellow gold, for example, it is possible to obtain ductile, deep drawing gold for hollowware and toilet ware; a corrosion-resistant spring stock for fountain pen nibs; a hard, high- tensile strength gold for handmade casework; spring temper wire for pin tongs and springs; alloys which cast well, and others with superior enameling properties.
Yellow golds offer the widest selection of properties and compositions. There is a yellow gold composition for virtually every jewelry requirement. The red golds, as a group, have a tendency to oxidize more rapidly when heated (in soldering or annealing) because of their high copper content. Karat golds can be quenched in water from the annealing temperature. This will give a softer and more uniform alloy than air-cooling. It should be clearly understood, how- ever, that quenching from the annealing temperature means drop- ping or plunging the karat gold into the water while the gold is still at temperature. Delaying the quenching (allowing the gold to cool off before plunging it into the water) can cause non-uniformity of hard- ness throughout the piece and the gold will not attain maximum softness.
Since it is possible to harden gold by raising the annealing temperature, the user of karat gold should know the proper annealing temperature for the particular compositionbeing processed. In general, red, green and yellow gold alloys are annealed at 1200F. (649C.).
In annealing wrought metals, under-annealing may create directional properties, and over-annealing may produce "orange peel" surface. On the other hand, in the annealing of cast pieces prior to precipitation hardening, relatively higher temperatures and longer times of anneal are suitable.
Annealing and hardening parameters have been worked out for each standard alloy, and best results will be obtained by following the manufacturers recommendations closely.
The high heat of annealing and soldering may cause surface oxides, or a condition called "fire", appearing as reddish streaks or blotches around the heated area.
Surface oxides can be removed by a 10 % sulphuric acid solution heated to about 180 F. (80 C.). Eight parts water to one part nitric acid brought to boiling may also be used for 10K and 14K golds. Where the sulphuric acid does not remove the scale readily a small amount of sodium bichromate may be added.
Fire affects particularly the lower karat golds and red golds because of their higher copper content. It can be prevented during heating by a coating of Handy 8z Harmans Handy Flux, which helps protect the metal surface from oxidation. Fire that is too deep for polishing out can be removed by dipping the gold briefly in a cold 25 % nitric acid solution.
Harman Gold Alloys
Handy & Harman manufactures a complete range of karat gold alloys in many forms, including casting grain, strip, wire, tubing, circles and blanks. These alloys are standardized to meet the most exacting requirements, and are carefully fabricated so that compositions and characteristics do not vary from order to order.
Handy % Harmans full karat gold alloys are supplied in the following karat designations: 10, 14, 18 and 23%. Yellow colors are available in the above karat groups, while white, red and green golds are available in 10, 14 and 18 karats. Their fine gold content ranges from approximately 41% to 99%.
Handy & Harman karat gold casting grain is fabricated in karat designations of 10, 14 and 18. Their gold content ranges from approximately 41% to 75%, and fine silver content from 5 % to 35 %.
Handy & Harmans karat gold strip is supplied in a thickness ranging from .004" to .250," and widths of ?" to 6."
Handy & Harmans "rolled square" gold wires are supplied in diameters ranging from .125" to .375." Round wires are available in diameters of .007" to .125."
Handy & Harmans circles (discs) are available in diameters ranging from ½" to 6," and from .007" to .100" in thickness.
Handy & Harmans rectangular blanks are supplied in a thickness ranging from .007" to .150," and from ½" to 6" in width.
Karat gold tubing is used in a wide variety of applications, including wedding bands, bracelets, clasps, beads, flutes and hoop earrings. The wall thickness will vary from .070" to .005," depending upon the particular application. Outside diameter has a range of 1 inch to .040," again depending upon end use. Generally, four alloys are commonly used in tubing; Yellow #2, Yellow #29, Yellow #515, and White #60. The Yellow #2 and #29 are excellent general-purpose alloys. Yellow #515 is used in thin wall applications, both for economy and to allow maximum hardness for a quality product. The flute industry has historically used 9K, 10K, 14K and 18K red golds. Tubing, like all mill products, is available in tempers ranging from Dead Soft to Hard as Drawn.
When ordering tubing, the following information must be provided for prompt and accurate delivery of materials.
l. Outside diameter and tolerances.
2. Inside diameter.
3. Wall thickness and tolerances.
4. Length, or by coil.
Handy & Harman has devised a simple formula that will allow you to know the weight of your tubing order: Outside diameter x 3.1416 x wall thickness X length (inches) X density = weight in troy ounces.
Investment casting is an ancient art, nearly as ancient as the Metal Age itself, which began with the melting of copper in various parts of the Near East, in about 4000 BC. The molten copper was cast in open, multi-compartmented, re-usable molds. The early production of ovens, molds and crucibles required the combined skills of clay- and metalworkers. These workers discovered that a wax model embedded in clay would produce a cavity when the clay was dried and heated and the melted wax ran out. The cavity could then be filled with molten metal to provide a metal replica of the original wax model. This "lost wax" process has remained popular for 6000 years, and has formed the basis of modern in- vestment casting, which sometimes uses newly developed materials, such as plastics, instead of wax.
Today, through the advances in the metallurgical sciences, the development of specialty alloys and sophisticated casting equipment, the process is a science in its own right.
Compared to hand crafting or die striking, casting has the following advantages: greater freedom of design, higher integrity of reproduction (especially of fine details), ability to undercut, higher strength, better control of color, and lower production costs.
Investment casting can be used for almost all gold alloys and practically every form of gold jewelry manufacture.
Successful casting involves three factors: 1) the proper design of the article, 2) selecting the most appropriate alloy and, 3) using the right casting technique.
The manufacturer must consider not only the aesthetic shape and color of the finished piece, but also how the article is to be made, so that the molten metal will fill the mold properly, and will cool with a minimum of porosity and stress.
a. Design the articles so that the casting will cool as uniformly as possible, and so that contraction takes place sequentially.
b. Avoid designs (like alternating thick and thin cross-sections), which tend to inhibit alloy flow during solidification.
c. Avoid acute angles and shapes, which can shift shrinkage directions abruptly.
d. All angles (inside and outside) should have fillets or rounds with radii equal to half the thickness of the section. Sharp angles cause "hot spots" and concentrate stress points. Caution: Fillets with too large a radius may cause shrink- age and weakness.
e. Avoid "X" type intersections. In- stead, stagger connecting arms for better flow of metal, and to reduce the overall volume of metal at each junction.
f. Avoid pointed details and thin edges, where possible, since they may not fill completely.
g. Design open holes so that they are no longer than four times the hole diameter. Blind holes should not be deeper than twice the holes diameter.
As a manufacturing jeweler you have many alloys from which to choose, so your choice must be a careful one, Factors to consider include fluidity, hardness, heat treatability, temperature range, and freedom from porosity and reproducibility.
Karat control is also of great importance, and should include a degree of reliability that is documented by assays. The alloy you select should have a proven record of performance, supported by research data and by production recommendations, which any caster can follow.
The ratio of new metal to remelt stock will vary widely, according to the casting technique. As a general rule, 60 % new gold with 40 % remelt will give good results for yellow golds; for white golds the ratio should be about 70 % new to 30 % remelt. These proportions work best when the alloys have had deoxidizers added by the producer. If, after several casting cycles, the alloy becomes darker, the percentage of new alloy should be raised until the problem disappears.
a. The aggregate weight of the sprues, trees and button should equal or exceed the weight of the article to be cast.
b. The cross-sectional area of the sprue should be equal to, or greater than, the cross-section of the article at the point of juncture.
c. The sprues should be long enough to position the articles away from any pools of heat, which often develop near the tree or base.
d. Whenever possible, the sprue should meet the article at its heaviest section. This is a critical consideration when casting white golds.
e. Light rings or bezels can hang directly from the button. For more intricate pieces, position the tree between the sprue and button.
f. Where a tree is used, its cross section should be at least twice as great as that of the individual sprue.
g. With high-temperature karat golds (primarily the white, nickel- bearing alloys), avoid direct impingement of the molten metal against the investment. Where possible, use a sprue, attached to the tree at a downward angle, away from the direction of the metal flow.
h. Allow for proper burnout time, as recommended by the manufacturer of the investment materials.
Porosity is recognized as the most common defect in products made by lost wax investment casting. As a precautionary guide, the following listing presents the major causes of porosity in order of their occurrence in the casting process.
b.Air bubbles in wax pattern.
c.Improper treeing of wax patterns.
d.Improper or incomplete wax burnout.
e.Flask (oven) temperature too high.
f.Contaminated or improper alloys in metal.
g.Overheated, oxidized metal.
h.Excess flux in crucible.
i.Unclean work habits.
Gold for the millions: The possession of gold in any of its forms, was, until recently, a rather exclusive privilege. However, an "accident" in a silversmiths shop more than 200 years ago set the stage for the popularization of gold putting it within the reach of millions. This accident led to the development of gold filled, which is an overlay of 10 karat gold or better bonded by heat and pressure to a reinforcing metal.
The silversmith was Thomas Bolsover, of Shefheld, England, who, while using a copper coin as a shim to hold a silver knife in a vise, discovered that after several hours of clamping, the copper had fused to the silver. This mechanical bonding process would later be used to fashion fine heirlooms (using mini- mal amounts of silver bonded to less costly metals), which not only exhibited the beauty of a precious metal, but was also affordable to a wide stratum of the population. The technique of mechanical bonding, taking its name from the place of its discovery, was called the "Old Sheffield Process," and when the amalgam was produced with gold or silver, the end product was called "gold filled" or "silver filled," respectively.
The process of bonding or fusing a thin layer of gold to a thick layer of base metal has several advantages. First, of course, is economy, since the precious metal can be only a few thousandths of an inch thick,
and still provide all the surface beauty of solid gold. Second, the base metal can be used to provide physical characteristics, like strength and hardness, far above those available from pure gold. And these support metals can be used in areas, which are subject to the most severe, wear.
Gold filled is produced by fusing a layer of karat gold to a suitable supporting metal (or alloy), using equipment that carefully controls pressure, heat and time. The bond produced is a permanent one. Next comes a series of rolling operations, which compress the strip into a sheet. Repeated rolling reduces the thickness of the material in such a way as to preserve the proportionate thickness of the gold and the supporting metal. Repeated rolling also serves to densify the gold, so that it becomes harder and more durable.
Gold-filled products must consist of at least one layer of a minimum of 10K gold. The karat gold layer must represent at least 1/20th of the total metal weight. Rolled gold plate is material consisting of a layer or plating of 10K gold or better, but the proportionate weight of the karat gold may be less than 1/20th (1/30th, 1/40th, or as the case may be).
Single plate strip: Gold is bonded to one face of the support material. This is the most popular form of gold filled in applications where one surface of the gold filled will be visible. Special rolled-on patterns can be impressed on the gold side to give extra interest and appeal. Some typical applications are watchband top shells, cufflinks and tie holders.
Double plate strip: Gold layers are bonded to both faces of the supporting material. Double plate strip is used on applications where both sides of the gold filled will be visible, or where the second side will be in direct contact with the skin. Some typical applications are pendants, charms and I.D. bracelets.
Solder flushed strip: This consists of a layer of gold bonded to one face of the supporting material, plus a layer of solder bonded to the opposite face. The thickness and type of the solder can be varied to meet a manufacturers specific need. This form of gold filled is ideally suited for furnace or induction soldering, as well as torch, and can affect significant production economies. Solder flushed strip finds wide application in the manufacture of earrings.
Gold-filled tubing: The process starts with a flat disc of gold-filled sheet. The disc is first formed into a "cup." This cup is then drawn over hardened steel arbors in special drawing presses, which further elongate the cup, until a long, seamless tube is created. Throughout the drawing process, the thickness of the gold layer remains precisely proportionate to the supporting metal.
Gold filled tubing becomes the stock from which many cylindrically- shaped objects are fabricated, such as pens, pencils and bracelets.
Gold-filled wire: This wire is made by inserting a core of supporting metal into a seamless karat gold tube, and fusing them together into a single rod. The round rod is then drawn repeatedly through reducing dies, until it reaches the desired diameter.
For special shapes and designs, the gold filled wire can be fed through hardened-steel rolls, which have patterns on them. As the wire passes through them, the patterns are transferred to the wire.
Typical applications include optical frames, rings and bracelets.
Solder filled wire: This wire is made by drilling a hole lengthwise through the center of the core, before reduction. The cavity is then filled with a solder core of predetermined size, composition and melting point, The filled core is then reduced, by stages, as in the manufacture of gold filled wire. The final diameter can be made as small as 0.005," with- out losing integrity of the metal proportions.
Solder filled wire is used almost exclusively by manufacturers of body chains.in Gold Filled
Composition (commercial brass or bronze)
This is a popular choice, as it has a yellow color similar to that of gold and has desirable physical proper- ties. It solders well, provides a good base for engine turning and engraving, and is easy on cutting tools.
Strong and highly corrosion- resistant, nickel is usually specified only where these qualities are essential. This is because nickels high hardness makes it relatively difficult to work.
Nickel silver (German silver)
This provides good strength, and is superior to brass in corrosion resistance. The most commonly used nickel silver alloys contain 10 %, 15 % or 18% nickel. Nickel silver contains no silver the percentage refers to the nickel content of the base metal alloy.
This metal is known for its strength and "spring" qualities, and is used where these qualities are important.
This is a nickel chrome alloy, which is very tough, and has excellent strength and corrosion resistance. Inconel, however, is relatively "hard" on tools.
This is a thin layer of pure nickel, placed between the gold and the base metal (usually composition or nickel silver). This layer helps protect against corrosion, although it is not recommended on applications, which require engine turning or engraving.