Decorative gold materials

Detailed reviews for the reader on the application technology, materials used [1,2], and history [3] are available. The scope of this chapter is to introduce the materials and application technologies associated with decorative gold materials, highlighting their origin, history, and chemistry. It is aimed at the reader with a scientific background who is curious about the development of this technology, and who may wish to pursue this area further. 

This chapter was written to enable the reader to obtain a broad overview of the materials and processes used in the decorative gold industry. Some observations can be made from the technology discussed, and some thoughts from the authors follow. 

However, it is hoped that recently developed gold materials (in particular gold nanoparticles) will allow for an expanded future product range capable of branching out into new markets such as the electronics industry for conductive applications, and the plastic/paper decorative sector, where low processing temperatures are required. 

Li et al. reported first on the decoration of hydrothermal carbon spheres obtained from glucose with noble metal nanoparticles [19]. They used the reactivity of as-prepared carbon microspheres to load silver and palladium nanoparticles onto then-surfaces, both via surface binding and room-temperature surface reduction. Furthermore, it was also demonstrated that these carbon spheres can encapsulate nanoparticles in their cores with retention of the surface functional groups. Nanoparticles of gold and silver could be encapsulated deep in the carbon by in situ hydrothermal reduction of noble-metal ions with glucose (the Tollens reaction), or by using silver nanoparticles as nuclei for subsequent formation of carbon spheres. Some TEM images of such hybrid materials are shown in Fig. 7.4. 

For insulating materials, on the contrary, the Fermi level lies in the gap, so that it is not detected on the photoelectron spectra. A possible calibration method stems from the gold decoration technique the binding energies can then be referred to the Au 4f doublet. This leads, however, to a poor reproducibility of the calibration Neither is the 1 s line of adventitious carbon a better energy standard. 

Jewelry, or pieces of metal, stone, or other materials worn for ornamental purposes, has existed for centuries and represents one of the oldest crafts known to humanity. Jewelry is a form of sculpture in miniature. Many pieces, if enlarged, would be successful decorative pieces. For our purposes, we address jewelry made of metal, although many other materials, such as beads, feathers, fiber, stone, wood, clay, paper, leather, glass, and natural objects, are used to make a wide range of modern jewelry. The metals most suitable for jewelry are the heavy metals, metals of high density, such as gold, silver, and copper. 

The corrosion products of noble metals such as copper and silver are complex and affect the use of these metals as decorative materials. Under normal atmospheric conditions copper forms an external layer of greenish copper carbonate called patina. Silver tarnish is silver sulfide (Ag2S), which in thin layers gives the silver surface a richer appearance. Gold, with a positive standard reduction potential (1.50 volts), significantly larger than that for oxygen (1.23 volts), shows no appreciable corrosion in air. 

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