Prof. Dr. Erhard Brepohl
Articles and Videos by Prof. Dr. Erhard Brepohl:
Cuttlefish casting is a quick and fairly accurate casting method. Its applications are limited only by the thickness and overall dimensions of the shell. It is difficult to achieve fine details on the surface of the casting, but this is offset by the richly complex texture that is a natural by-product of this method.
Though sand casting has been largely replaced by centrifugal casting in recent decades, for hundreds of years it was the most popular of all casting methods. It still plays an important role in the production of large metal forms, and can offer the advantages of low cost, quick results and ease of duplication to those goldsmiths who take the time to master it. Though sometimes thought of as coarse, sandcasting can yield results that are as fine and true to detail as any other casting method.
As important as the gravers are, it is hard to understate the importance of the devices used to secure work while engraving. Or to say it another way, even a properly sharpened graver in experienced hands will be difficult to use if the workpiece is sliding across the bench. Knowing this it is not surprising to find that several tools have been developed to hold onto the work for cutting.
Many industries have need of specialized engravers, for instance those who make dies, who cut stones and glass, and others who carve reliefs. Though a goldsmith might call on a specialist for certain jobs, it is useful to have a general understanding of the technique and sufficient skills to use gravers for simple everyday tasks at the bench.
Niello is a deep black metal mixture that is fused onto metal for decorative effect. Though worked on three-dimensional objects, the effect might be considered graphic because it relies primarily on shape and pattern. The contrast of the lustrous black inlay against either matte or polished metal is striking and has earned niello a special place in the arsenal of decorative techniques.
There are many techniques in which contrasting metals are placed side by side. Those that can properly be called inlay require a mechanical attachment to secure a soft material into a harder one.
For more than two thousand years, goldsmiths have fused glass onto their work for color enrichment. Wonderful enameled work can be found from many ancient cultures, providing familiar icons of the technical skill and aesthetic sensibilities of their makers.
In the twentieth century there can be little doubt that electroplating is the best way to develop a gold coating on a metal object. It provides successful results in many colors and can be adapted to one-of-a-kind or mass production. Knowing this, it might seem peculiar to devote the following section to the ancient art of fire gilding. It is more time consuming than modern methods, it requires more material, there is a greater risk of failure, and it is a health risk unless performed under ventilation. Why then should it be included?.
It is not uncommon for moving parts to wear out. This is to be expected because of increased friction as parts rub against one another. A common example can be found in connecting rings such as the jump rings that attach a charm to a bracelet or a pendant to a chain. If a section of the ring is worn thin it is usually best to discard.
A ring fits well when it is no longer felt on the finger. If in the course of time the size of the finger changes or if the ring is to be fitted for another wearer, a sizing of the ring is necessary. The first step is to determine the finger size, which is done with a ring sizer, a set of about 30 steel rings in graduated sizes.
The purpose of precious metal testing is to determine, first, whether a given sample is precious or base, and, second, to determine what proportion of an alloy is precious. Sophisticated equipment is used in a precious metal laboratory to determine content and purity values with great precision, but our attention here is given to methods a working goldsmith can use in the studio to determine metal content to a practical degree of accuracy..
The principle of this ancient, valued procedure is described here because of its historical interest, and with the thought that young people coming into the field should be aware of the basic procedures of the trade, even though they may not pursue them. In the case of precious metal refining, it is generally more efficient to send scrap to a reputable refiner where sophisticated equipment and years of experience will insure accuracy. In addition, the procedures described below use dangerous acids that mandate industrial quality ventilation and safety precautions, which makes the decision to send out refining chores even more compelling.
The revival of granulation in our century has been accompanied by many wrong ideas and misunderstandings, many stemming from the incorrect notion that the secrets of a mysterious process were long lost. To better understand granulation, we should therefore start by examining the myths and laying them to rest.
Because titanium behaves somewhat differently than the standard metals in the goldsmith’s workshop some special attention to its working is in order here. When sawing, begin the cut with a very light stroke, and increase the pressure only when the blade has securely caught. The sawblade can be protected with a lubricating grease, but even with this precaution it will dull quickly. Titanium can be worked with standard files, but.
The pleasure and challenge of including gems in a jewelry object (beyond the intrinsic beauty of the gem, of course) is to resolve the various factors that come into play. A well designed setting must achieve several goals simultaneously it must secure the stone, enhance both the gem and the metal object, it must stand up to wear while protecting the stone, and it should harmonize with the aesthetics of the piece. One of the first decisions about incorporating a stone is to determine whether it is to be the focal point of a design or a component in service to some other more dominant aspect. Clear thinking on this fundamental question will assist in the many decisions that must follow, including proportion, style, texture, color, location and size..
In practice an experienced eye will usually be able to determine by color and luster whether a piece is made of silver, a base white metal such as nickel silver, or a precious white alloy such as white gold or platinum. If this can be determined by eye, it’s usual to proceed directly to the qualitative test.
The terms repousse and chasing are often confused and not without good reason since the two techniques are often worked together. One might as well think of slipping and sliding to realize how difficult to establish a clear definition particular to each process. In general we might think of repousse as primarily a relief and chasing as more often an intaglio (2-D or linear) technique.
Rolling can be thought of as a local, or isolated, deformation process during which thickness is decreased, length increased, and width remains unchanged. Drawing is different from rolling in that the pressure of drawing it not transmitted through the turning action of the mill, but instead depends on force directed locally at the area of compression. This means the amount of possible drawing force is limited by the tensile strength of the material, a fact that is particularly evident when drawing thin wires..
Etching uses chemical corrosion rather than mechanical force to selectively remove metal. Simply put, the idea is to cloak parts of an object with an acid-proof paint then submerge the piece in acid. The caustic liquid eats away at exposed areas to create a relief. When the proper depth is reached the piece is withdrawn, rinsed and cleaned to reveal a pattern of raised and lowered sections. The process can be used for delicate linear drawings, for bold reliefs, for letters, and as a preliminary step for enameling, niello, or inlay.
When precious metal is heated to temperatures approaching its melting point there is a short span during which the outer layer or skin begins to melt while the interior remains solid. Or, to say the same thing technically, the interior remains in the solidus zone while the surface regions enter the liquidus range. The effects are to create an uneven reticulated surface and to allow pieces to join by welding. Every goldsmith discovers fusing, usually by accident and usually as a mistake, when pieces being soldered are overheated.
The first requirement of all catches is that they secure neckpieces and bracelets in such a way that they will not fall off the wearer. Once this is accomplished, there are other concerns that should be addressed. Making catches requires a high level of skill, but the rewards, in both technical and aesthetic satisfaction, make the effort worthwhile. The following examples should only serve for inspiration, and may need to be altered for your particular use. It is part of the creative process when designing and drawing the piece to create the most suitable catch and to incorporate it into the entire design of the work..
Box catches lend themselves to a wide range of shapes and are frequently used on chains, bracelets and cuff bracelets. They combine security with ease of use and the ability to be adapted to the needs of each design. After mastering the basics, it becomes an appealing challenge to a goldsmith to design a box catch uniquely suited to each new piece. The basic ingredients tongue, box, snag and trigger will be introduced through the basic box shown here, and they will reappear in each permutation.