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Granulation is a decorative technique whereby multiple gold or silver spheres are attached to the surface to create a specific decoration. Technically, this can be done with or without soldering, but "true' granulation is often associated with not using solder. While possible with traditional soldering, the join formed with traditional granulation (reaction soldering) is much more delicate and hidden. The earliest evidence of the technique dates back to around 2500 BC in south Mesopotamia. Today the technique is commonly used in both gold and silver jewelry. Gold granulation is usually practiced in higher purity alloys, from 18–22K (750–917). "True" Granulation, or reaction soldering, does not involve a conventional soldering alloy, but uses a copper salt/glue. It is a form of surface or localized alloying that happens on heating. Granulation in Gold and Silver The granules and the "back plate", onto which the granules are attached, must be carefully prepared. For the granules: Gold or silver granules are made by cutting a coil from a fine wire wrapped around a mandrel. The wire is then placed in a crucible filled with charcoal powder and heated. As the wire melts, it will form a sphere. A spherical shape minimizes the amount of surface area, and therefore the energy of the alloy. This is often described using the concept of surface tension. The charcoal powder helps to form perfect globe shapes, and helps prevent oxidation. The granules can then be pickled to remove any surface oxide which may have formed. For the granulation itself: The granules can be positioned onto the surface using a water-based glue containing a copper salt and then dried. They can then be heated and the granules fuse to the piece. Science of granulation – Reaction soldering On heating: (100˚C/212˚F) – Copper salt is oxidized to Copper (II) Oxide. (600˚C/1112˚F) – The glue burns and carbonizes. This creates a reducing area and converts the copper oxide to a metallic copper. A thin copper layer forms on the surface of the surface and granules. (850–890˚C/1562–1632˚F) – The copper diffuses with into the gold or silver surface. This leads to a reduction in the melting point of the alloy. The two surfaces now have a lower melting point than the rest of the alloy. The surfaces then melt very quickly, long before the rest of the alloy, and so a metallic bond is formed between the two pieces. The heat is removed and the join solidifies, with the rest of the alloy "untouched". Thus, we get a self-soldered joint known as reaction soldering or transient liquid-phase bonding. Forming a solid connection To ensure a strong bond between the surface and the granules, it is necessary to form a thick enough join between the two of them, known as a "neck". The correct ratio between energy and time, between the heat and the duration of heating is crucial: Insufficient heating is insufficient to form a strong connection Overheating will causes the granules to melt into one another and into the substrate. The joining phase takes the least time of the entire process of granulation, but at the same time it is certainly the most difficult. Granulation by plating Granulation in high-karat gold, and sometimes in silver, is often performed using extra steps. Instead of using copper salts with the glue, the copper is applied directly to the granules. The copper can be applied by electroplating, using an acidic solution. This allows careful and precise control of the amount of copper applied. Fully pre-copper plating the granules and the substrate also has some disadvantages, because we cannot remove the excess copper which isn't used to make the connection: Excess copper causes the surface to sweat. The whole sample needs heating for the granulation process to work. Heating an entire sample for decorative granulation is not feasible. Since the granules are not glued onto the surface, the little balls will roll off as soon as the object moves. Even if this is achieved, upo n heating, the granules will heat quicker than the bulk object. They will quickly come to their melting point and melt away while the surface of the object will not be warmed up enough to make the connection. It is often easier to heat the object and granules with a large propane/compressed-air flame, traditionally used for annealing and soldering silver hollowware. Using the torch in the “right” way allows to bring only a very small area to the required temperature for granulation. Common problems Read more by David Huycke (Santa Fe Symposium):
- Why is there porosity in my casting?
Porosity in casting is a common defect and can usually be attributed to one or two main causes. It is often easily rectified. Here's a quick question and answer to try and help you solve the issue. #1 – What do the pores look like? Are the pores round and spherical or are they more tree-like in shape? Round and spherical pores are indicative of gas porosity. Go to #2. Otherwise, go to #3 #2 – Gas porosity – are they throughout the sample or just at the surface? If they are located at the surface only (shown left), the porosity is likely caused by the evolution of gas due to a reaction at the mold wall. In general, clean burnout of the mold, use of cleaned scrap (especially recycled casting sprues) in the melt charge, and lower casting and/or flask temperatures will reduce the probability of gas porosity. For more details, see: D. Ott, Handbook on Casting and Other Defects in Gold Jewellery Manufacture (London: World Gold Council, 1997). If they are located throughout, the porosity is likely caused by dissolved gas in the alloy. Ensure high-quality start material (>99.9% high-purity metals or Pure master alloys) and that the material is all dry before melting. #3 – Shrinkage porosity? If caused by shrinkage, then this is common for investment cast products where there is essentially insufficient liquid able to fill the mold during solidification. It is important to carefully consider mold design, specifically the diameter and positioning of sprues.
- Welding in Jewelry
Welding involves joining two pieces of metal together by melting them with or without filler material. The pieces being joined must be in good contact and heated locally to melt the joint surfaces together. The metal will then solidify, forming a metallic bond between the two parts. Microstructure of a weld The microstructure of a weld has some key features: The melted metal will solidify a classic dendritic-cast microstructure Around the weld is a heat-affected zone (HAZ) which absorbs heat from the molten metal during solidification. The size (width) of the weld zone will depend on the heat source used and the properties (conductivity) of the weld materials. A large gas torch, for example, will produce a larger (wider) weld zone than a laser, where the heat energy can be finely focused and is more intense. Properties of the Heat-Affected Zone The area around the weld will not be melted but heated to a high temperature. As a result, we may see a great deal of grain coarsening and potentially the transformation into meta-stable high-temperature phases. Grain coarsening will ultimately lead to a softer, less hard area Meta-stable phases are typically brittle. So a weld zone may have mechanical and corrosion properties that differ from the normal parent metal unaffected by the welding. We may also expect some surface quality degradation due to melt turbulence and oxidation, possibly with some porosity due to expelled gases. Types of Welding Tungsten Inert Gas (TIG) and electrical resistance spot welding use electric current to generate heat: TIG welding – the current strike an arc between the tungsten electrode and the workpiece. Plasma arc welding – A plasma is formed from the ionized gas surrounding the electrode, generating considerable heat. Laser Welding – Heating can also be accomplished by an electron beam or by a laser beam. Why is Laser Welding so popular? Laser welding has become very common in the jewelry industry. This high-energy source allows very fine and deep welds. This means: Repairs can be made close to set gemstones without damaging them (no removal necessary) due to a small heat-affected zone. It is quick and precise. It can be done in the air (no special atmosphere or flux is necessary), and there is little fixturing required. Several welding operations can be done on the same workpiece without fear of re-melting earlier joints. Filler metals can be used if desired, for example, in filling open porosity; these are normally of the same alloy as the workpiece, thus giving no problems with color matching or karatage mismatch. It is particularly suitable for pure precious metals (e.g., 24-karat gold). Laser welds tend to be stronger and more ductile than soldered joints, with little porosity. There are no toxicity problems as are associated with cadmium in solders. On the other hand, laser welding can be more time-consuming than soldering, and the welds may have a bulbous overlap surface that will need grinding and polishing. As stated earlier, it is also a line-of-sight method. Laser welding is often used for decoration by granulation and is commonly used for making chain links in situ.
Other Pages (10)
- Casting Techniques | Science of Jewelry
Fundamentals Want to understand more how materials behave from their structure at the atomic level. Here is a brief introduction to the underlying principles of metallurgy – the scienfitic study of metals and their properties. We've come a long way since the bronze age! Oct 10 2 min It's cracked! How on earth did that happen? Oct 10 3 min An introduction to working a metal after casting Aug 1 3 min An introduction to Phase Diagrams Jul 28 4 min The science of strengthening metals Jul 28 3 min Why do some alloys get harder during heat treatment? Jul 27 3 min What is a metal? The Basic Structure Jul 27 4 min What is alloying? Surely, pure gold is best? Jun 1 3 min What happens when you deform a metal?
- Home | Science of Jewelry
Welcome Explaining the science behind the art that we all know and love. We aim to help customers, store agents understand better and bench-top jewellers achieve more. Sterling Silver Globe constructed by Granulation Courtesy of David Huycke Courtesy of Marc Adwar Our Mission The science of noble metals explained simply... for everyone Whether you're making intricate pieces, selling or buying them on the shop floor, or developing jewelry materials and techniques for the future, understanding the principles of what jewelry is made of, how it's made, and why the materials behave as they do is essential. At JewelryScience.com, we aim to explain these principles in quick, easy-to-understand 3-5 minute reads with minimal jargon. Any we do use are highlighted in italics! We're a group of metallurgists and artisans who specialize in precious metals and want to share our knowledge. Want to understand something that isn't yet covered? Let us know! We'll add it as quickly as we can. About us For enthusiastic consumers Want to learn more about what you're buying? Learn what is actually on your wrist, and why one piece is more expensive than the other. Learn More Metallurgy for the Jeweller We've split up all the science of metals (metallurgy ) into 6 key topics relevant to jewelry. They cover the fundamentals of metallurgy , to what each material is made of (alloys ), and what the future of metallurgy may hold for jewelry design and manufacture. I f you just want to browse our site , then please click here . Alloys & Composition 18K Gold contains more elements than just gold! An alloy contains two or more elements. The exact quantity of each element (composition ) is carefully controlled to make sure the desired properties are achieved. Find out more Casting Techniques The type of mold the liquid metal is poured into and how it is poured can have a substantial effect on the final appearance and properties of the final piece. Many of these techniques have been optimized over hundreds of year. M etallurgists can now explain why we do what we do. Find out more Metal Working & Heat Treatments How you deform a metal and heat it can dramatically affect the final properties and how much you can shape it. Joining two or more pieces of metal can be done in several different ways – choosing the right one is important for a long-lasting jewelry piece. Find out more Techniques There are many techniques that produce stunning jewelry, but many people have never heard of them. Have you heard of Mokume Gane? Find out more Principles of Metallurgy Want to understand more how materials behave from their structure at the atomic level. Here is a brief introduction to the underlying principles of metallurgy – the scienfitic study of metals and their properties. We've come a long way since the bronze age! Find out more Technologies of the future Heard of 3D printing? Powder processing and Metal Injection Molding? Bulk Metallic Glasses? There are many exciting areas of development that could soon reach the jewelry bench and your wrist. Find out more Troubleshooting Got a specific problem with the metal you're using, and don't know what's going on? We'll put all our case-studies here, or please get in touch! Learn More Our Story Courtesy of Chris Manning How it started At the 34th and final Santa Fe Symposium, there were many discussions about in what format the Symposium should survive in. From these fruitful discussions, this website emerged as a possible way to spread the knowledge shared at the symposium further and all the way to the consumer. About us Latest Content 3 min Granulation 0 Post not marked as liked 1 min Why is there porosity in my casting? 0 Post not marked as liked 2 min Welding in Jewelry 0 Post not marked as liked Supported by The Jewelry Symposium The successor to the Santa Fe Symposium Contact Us Name Email Phone Address Subject Message Submit Thanks for submitting!
- Casting Techniques | Science of Jewelry
Working, Heat Treatments & Joining How you deform a metal and heat it can dramatically affect the final properties and how much you can shape it. Joining two or more pieces of metal can be done in several different ways – choosing the right one is important for a long-lasting jewelry piece. Oct 10 2 min It's cracked! How on earth did that happen? Oct 10 3 min An introduction to working a metal after casting Aug 1 3 min An introduction to Phase Diagrams Jul 28 4 min The science of strengthening metals Jul 28 3 min Why do some alloys get harder during heat treatment? Jul 27 3 min What is a metal? The Basic Structure Jul 27 4 min What is alloying? Surely, pure gold is best? Jun 1 3 min What happens when you deform a metal?