One of the revolutionary features of direct metal 3D printing techniques such as selective laser melting (SLM ^TM) is the capability to manufacture jewelry from platinum alloys, which are notoriously difficult to cast because of their high melting temperature and high reactivity with the crucible and investment mold materials. These material attributes of platinum have the consequence of high production costs, the need for specific furnaces and the incidence of frequent defects in the resulting jewelry products, making SLM a practical alternative to casting. In this paper, the revolutionary scope of the SLM technique in platinum jewelry production is compared to traditional production techniques. The technical aspects as well as the economic/financial implications to the production process are considered in order to understand whether and how much the introduction of the SLM technique constitutes an improvement in platinum jewelry manufacturing.

The production success of lost-wax casting depends not only on the process parameters of the casting systems but also on the chemical composition of the alloy, which strongly affects its behavior in the liquid state. In addition, potential solid-state phase transitions alter the alloy’s mechanical properties. The characteristics of the alloy in its liquid state and its density changes due to solidification can affect the form-filling capabilities and the quality of the pieces. The aim of this research is a deeper understanding of the relationships between the chemical composition, the main thermodynamic characteristics, and the castability of an alloy in investment casting in order to create an instrument capable of predicting its technological behavior in advance, thus avoiding the expensive process of characterization. The analysis of the relationship between alloy composition and castability was carried out by means of traditional investment casting and by using Differential Scanning Calorimetry (DSC), Thermogravimetric analysis (TG) and Dilatometry (DIL), using the simplest binary alloys up to the more complex formulation of some gold alloys suitable for jewelry making.

As part of the fourth industrial revolution, the direct 3D printing of jewelry in precious metal deserves a constant state-of-the-art analysis to see if and how the strengths of this technique should be exploited. Why should jewelry makers decide to use this technique for their production? More precisely, the pragmatists would like another answer: When does this technique add more value compared to traditional investment casting? In recent years, our research path included printing strategies, supporting techniques, and examined at different levels of depth the chemical and physical characteristics of the precious metal powders used. This paper will look back at the technological evolution of direct 3D printing of jewelry with a more practical and operational eye, share our experience and give an honest analysis of its strengths and weaknesses. This detailed examination of the whole work done by Progold will be told through the viewpoint of one who exclaimed, "WOW!" when first introduced to 3D printing and will try to answer when and why it is worthwhile to print a piece of jewelry.

Direct metal printing is a game changer for creating innovative jewelry. Selective laser melting (SLM™) allows researchers to get creative and think about new materials. This research puts new and different products to the test, exploring fresh horizons for SLM™ utilizing amazing materials for jewelry applications. Additive manufacturing by selective laser melting provides the opportunity to combine materials with very different properties in otherwise impossible ways. What other astonishing new possibilities await as we learn about the surprising properties obtained?

In the world of direct additive manufacturing, Selective Laser Melting (SLM™) of powdered metal is currently one of the most attractive new technologies with potential to replace lost-wax investment casting because it enables the production of items with high geometrical complexity which are light and customizable. In addition, it provides several environmental advantages. In previous testing, improving the quality of items was achieved both by selecting best construction parameters and by developing alloys with greater laser absorption. In this work the dimensional accuracy of actual jewelry items is assessed and the possibility of making lighter items while maintaining adequate structural strength is explored. In addition, the best working parameters for red-gold and platinum alloys were studied. Dimensional accuracy was assessed by building a metal structure and an actual pavé ring. Then the geometrical conformity of the SLM ring was compared to the original design. The roughness of the metal section, metal density, metal homogeneity, accuracy of ornamental details and quality as a function of orientation on the build platform will be reported.

The results previously obtained with gold alloys for selective laser melting (SLM) underlined the key role not only of process parameters but also of powder chemical composition for producing quality precious metal jewelry. This paper illustrates the effect of some selected chemical elements to improve laser radiation absorption and to favor the melting of metallic particles. In addition, the action of the structure and morphology of the supports was examined in order to optimize their density and maintain an adequate thermal dissipation of laser energy.

This paper is a development of the results presented at the 2012 Santa Fe Symposium®. The effect of the most representative variables of the Selective Laser Melting (SLM) technology on the quality of final products is evaluated by means of the design of experiment approach (DOE). The variables taken into account are laser power, scanning speed and thickness of the powder layer. The aim of this paper is to identify the chemicalphysical characteristics of the powder that ensure the best results of the SLM technique. Analysis of the influence of chemical composition and powder particle size distribution on porosity and roughness of the final items is specifically studied. This work describes the progress obtained with SLM technology in the last year, and evidences the importance of optimising process parameters. All presented results were obtained using precious metal alloys.

Selective laser melting (SLM) of layered gold powder is a rapid manufacturing (RM) technology capable of turning a CAD model into a jewel without intermediate steps. As with any new technology, giving concrete and tangible form to concepts requires research and development and as Strauss (SFS 2009) points out, issues that can arise with RM jewelry regard powder quality and availability. This paper focuses on these issues together with laser power, laser scanning speed and the thickness of powder layer. A design of experiments (DOE) approach was used to characterize the influence of those variables on a 18K gold powder with reference to physical and chemical attributes, surface roughness, defects, and mechanical properties. A comparison of a series of specimens produced by SLM and lost wax casting will be presented.

Data about the characterization of 18ct gold alloys were presented by Progold at the 2010 Santa Fe Symposium. In this paper, we are going to discuss the chemical and physical properties of 14ct red, yellow and white gold alloys. As with 18ct gold alloys, knowing the alloys properties enables us to choose the most suitable composition for each particular production process. Colour is fundamental to the selection of a gold alloy, but how to get the desired color and favourable working properties is a question.

Knowing gold alloys characteristics enables to get precious information for selecting the most suitable alloy composition for each particular production process. Obviously, in the case of gold alloys, color plays a fundamental role in the selection of the composition to be used, but in all cases minor additions of some specific elements can contribute to improve some characteristics that are important in the production process. On the basis of these considerations, we decided to determine the chemical and physical properties of several 9, 10, 14 and 18 ct gold alloys. The aim of this work was to correlate the characteristics of each alloy with the chemical composition, to be able to select the gold alloy representing the optimum solution for the different practical uses. Considering the high cost of the alloys, we have refined some methods for evaluating the properties of precious alloys (or, better, we improved evaluation methods already used in different industry sectors), to obtain the data required to achieve this goal.

Hot tearing is the formation of a fracture in a metal casting during solidification, as a result of hindered contraction. In this study we tried to evaluate the hot tearing susceptibility of different silver alloys with 925‰ fineness. Several studies on hot tearing susceptibility of casting alloys are known, but we have not been able to find information on precious alloys. Therefore we wanted to characterize 925‰ silver alloys, that, according to our experience, are more prone to this kind of problem. A classic 925‰ silver alloy was taken into consideration, and we evaluated the effects of additions of other elements. We compared the different behavior of binary, ternary and quaternary alloys, with and without small additions of elements such as deoxidizers or grain refiners. Besides, we carried out a metallurgical analysis on cracked areas, trying to correlate the behavior of the alloys with their microstructure. This paper is a part of a wider research aiming to obtain silver alloys with high resistance to tarnish and a reduced tendency to hot tearing.

The daily routine of the goldsmith is plagued with unexpected problems such as random casting defects, which are very difficult to diagnose properly. This often causes a big waste of time and useless attempts to find the right solution. From our archive of defect analyses, collected over a ten-year period, we selected cases involving hard spots commonly occurring and difficult to diagnose correctly with the resources normally available in a goldsmith’s laboratory. It can be stated that the usual definition of hard spot actually identifies defects which, even when displaying the same appearance (under the naked eye or at low magnification), are a consequence of different causes. Basing our assumptions on such considerations, we sketched a detailed classification of various classes of hard spots, providing a series of causes and possible solutions.

The knowledge and the current testing methods regarding silver tarnish phenomena are not guaranteed to provide measurable evaluations of the phenomenon itself. Presently, all the formal and suggested tests are unable to demonstrate with any certainty what actually occurs, and they are especially unable to provide objective data. In fact, the tests are always carried out using a parallel reference sample, and so, provide only viewable, empirical data. Furthermore, the assumption is that once a minimum change in the test conditions takes place, the results become completely distorted. By following a more scientific method this paper will investigate more deeply into our knowledge of the chemical interactions that provoke the tarnish phenomena. The goal is to provide more trustworthy and repeatable data.

The term hard spots usually indicates the imperfections displayed on the piece surface after polishing. Basically they are high and hard relief spots which the mechanical finishing cannot eliminate, but usually stresses even with more force. In fact by insisting on polishing the hard spot zone, the material around the defect is removed, since it is tender. The result is to have hard spots that can be visible to the naked eye. The problem is that these defects, mostly, can be individuated only after polishing, therefore together with the damage due to the piece removal there is also all the time took to produce and finish the piece. The causes on the rampage which usually give birth to this defect are several. In this work the most common origins of hard spots growth have been analyzed and reported. One of the main causes surely is the presence of impurities in the raw materials used. When gold items are produced everyone (producers and final users) pay very careful attention to the gold content, especially that the gold composition corresponds to the mark printed, while on the other hand, no one pays attention to impurities, i.e. to what is no gold and it is not purposely added neither the pure gold ingot nor the master alloy. Such impurities can have very serious consequences on the quality of the items produced, like for example the hard spots growth.

Practical experience shows that gold alloy castings with homogeneous composition (and fineness) can only be obtained if some specific rules are respected. When the producer does not utilize the best practices for the preparation of the material, inhomogeneous castings could be obtained that originate jewelry pieces that do not comply with the claimed fineness. In this work we considered the homogeneity of the castings (obtained by means of investment casting or ingot casting) produced with different practices, i.e. with or without a pre-melting operation. The experiments have been carried out with alloys of different fineness and color. Our experiments showed that pre-melting guarantees a better composition homogeneity in all parts of a casting.

It is well known that in the investment casting of gold alloys silicon enables to obtain better mould filling and deoxidised castings. Up to now it has been believed that silicon as alloying addition or through the formation of SiO2 could be sufficient to explain the deoxidised appearance of the cast tree and the good filling of the mould. Preliminary analyses suggested that silicon dissolved in the liquid phase could form a compound with high surface tension that can form a thin film on the outer surface of the molten metal. This film restrains the evaporation of zinc and other metals, whose evaporation temperature is lower than the temperature of the molten alloy. In the case of investment casting, this film minimizes the contact between the components of the alloy and the mould wall, even if a reaction with calcium sulphate and/or its decomposition products (oxygen and sulphur dioxide) cannot be excluded. It is presumed that the reaction between the components of the alloy and the decomposition products of calcium sulphate will be minimized and that the thin film will facilitate the flow of the metal on the surface of the mould cavity, making mould filling easier.

Traditional 22ct yellow gold alloys (Au-Ag-Cu-Zn) allow obtaining low hardness products (about 70-80HV), not hardenable by means of heat treatment. Low hardness values involve the obtainment of items easily deformable both during the production cycle, and as finished product (easiness of breaking and indentations during daily use). The possibility of having a hardenable 22ct alloy, after proper heat treatment, guarantees some advantages both in practical terms and in economical ones. In fact, in addition to the possibility of working the items with more ease (as they are more resistant to indentations), some processes otherwise excluded can be introduced, such as treatments by mechanical finishing or brushes, which allow obtaining a high brightness. Then, we analyzed different compositions, to try and harden a 22ct alloy, and we succeeded in determining a formulation allowing a double hardness than those currently available (that is up to 170HV).

The definition of the colour of a finished product’s surface made of a gold alloy is mostly very hard, and it makes sense only if it is referred to a series of samples taken as terms of comparison. The Swiss organization “Normes Industrielles de l’Horlogerie Suisse” was the first one which established, in 1966, a series of standard compositions of gold alloyed 18 ct, named with the codes 2N, 3N, 4N and 5N. Afterwards, the French and German goldsmith’s industry conformed themselves (even if with some changes) to these standards until the redaction of the European EN 28654 rules. Such rules are the adoption of the ISO 8654.

Several 14 ct red gold alloys for investment casting with different composition have been studied and compared. A 585Au-80Ag-335Cu alloy that is particularly used in Russia has been taken as a reference. Starting from this composition, several different alloys have been formulated, with the addition of different amounts and combinations of different alloying elements, like zinc, gallium, indium, silicon and iridium. The different additions have been balanced, in such a way to keep a colour similar to the reference alloy. Different characteristics of the studied alloys have been evaluated, that are relevant to investment casting, i.e. shrinkage and gas porosity, grain size, mould filling ability, melting temperature and range and resistance to oxidation.

Most of the history of human being, with the born of civilization, can be described also through the progress of the production processes, which became, time by time more complex. The discovery, the research and the adjusting of the exploiting techniques of new resources have given their contribute to such progress. Otherwise speaking, the history of the human being can be described also as the exploitation of the mineral resources and especially of metals. The brightness features, the easiness at working, the stainlessness and the fastness, made Gold play a special role in history with regards to other materials gifted by nature. During the years, its employ has widened into different fields: for example in the monetary field it is still considered as a reserve property; in the technological field, thanks to its good capability to conduce electricity and its stainlessness it is very much used in electronics; at the end, it is employed also in the medical field thanks to its chemical inertia and the low risks for the human health. The field, though, where Gold has been always playing a predominant role is the one of the production of precious artefacts. From 5000 B.C, in fact, the capability to remain shining without never loosing its brightness, the particular features of malleability and the very much appreciated chromatic shades, have made of Gold, the mostly used noble material in the jewellery production. The main aim, in the jewellery world, is all the time to reach the aesthetical perfection, by producing artefacts which are a union between beauty and quality. As it happens in all the production processes though, even in the production of golden alloys defects can appear which draw to scrap the product or to the customer dissatisfaction. Therefore, especially in this field it is important to know and avoid defects. The correct procedure, when a problem is faced, is to analyze it in order to take precautions to eliminate the causes and to prevent a further reappearance. This turns out to be possible only if the defect is very well identified and the causes are known. This job is aimed to collect in a unique handbook all the notions regarding the defects typologies which can be produced in the jewellery production.

Recrystallization affects both the structure and the mechanical properties of metals. The knowledge of recrystallization conditions for gold alloys is very important for optimizing the production process. Recrystallization conditions (temperature and time) depend on the type of alloy and the degree of deformation. The following methods for determination of recrystallization characteristics will be compared: hardness measurements, metallographic investigation and differential thermal analysis. Samples are heat treated in cycles with temperature and time as variables. We will take into account 14 ct yellow gold alloy. They are tested with different procedures to allow the comparison of methods for determining recrystallization characteristics.

The metallurgic aspect of the goldsmithery processes was disregarded especially in the past favouring so a higher attention of the artisans to the aesthetical and stylistic aspects of their creations. This involves so an empirical approach and oriented to the minimization of costs in the castings preparation, instead than a conscious approach to all those problems connected to a casting process or their possible solutions. It is necessary to remind that great part of the defects are in fact related to the rough planning of the feeding system, which is finalized to save resources instead of obtaining a defectless casting. The preparation of the casting, instead, should take into consideration a whole series of kinetic and thermodynamic aspects together with the solidification of the cast. These two phases are fundamental for the global economy of the casting process and their correct functioning grants the final quality of the investment cast items.