The choice of materials in any project is important. Sometimes the required properties to execute a design dictate the material, sometimes the desire to use a material dictates the project and its limitations. Either way, the materials are as important to the design as the design itself. No matter which material is chosen, some compromises must be made.
Sterling has been the metal of choice for jewellers and metal smiths for centuries. The Sterling Standard was codified in 1275 during the reign of Edward I, but the alloy had been in use on the continent, and in Britain, for centuries already. The alloy is defined as being 92.5% silver, and 7.5% other metal, usually copper. Its very easy to work with, relatively inexpensive when compared with gold and platinum, but does have some limits.
The limit most people are familiar with is tarnishing. Sterling reacts to the sulphur in the air to form a sulphur oxide on the surface. It's a dull gray colour, and takes away from the look of the piece. Anything made in Sterling will require polishing and/or protecting, to remain shiny. A related issue is fire scale. Whenever heat is introduced, it accelerates the oxidation process. When soldering Sterling, flux is used to protect the metal from oxidation. Any part which isn't coated receives a light gray layer of fire scale. It must be removed either by sanding and polishing, or soaking in acid to dissolve the oxide layer. Either way, additional finishing work is required. The other issue I encounter with Sterling is how soft it remains after being heated. Once the piece has been cast or soldered, it remains in an annealed state. The metal is quite soft. The only option to harden the metal again is to work it, usually by hammering it. That's fine if you're raising a cup, but is an issue for making a pen clip.
If I'm going to use any Sterling in a project, I will usually buy it in either sheet form, or casting grain. If I need wire or tube, I will make them specifically for the project.
A number of new alloys were created during the twentieth century to combat the primary issue with Sterling, tarnish. Argentium was invented in the UK in the nineties by Peter Johns. It changes the Sterling alloy slightly by increasing the silver content to 93.5% (therefore still qualifying as Sterling for hall marking purposes), using copper for most of the rest, except for a small amount of germanium. The germanium changes a few characteristics of the silver in very significant ways.
The primary advantage is the layer of germanium oxide which forms on the surface instead of sulphur oxide. It is clear, and doesn't affect the polish of the silver. It also inhibits the forming of sulphur oxide. The result is a metal which does not tarnish very quickly. The same effect prevents fire scale from forming during soldering operations, saving time and effort during the finishing process. I have pens which are a few years old now, which have required no polishing. The second advantage of the germanium is the ability to precipitation, or heat harden the piece. If a pen clip is cast from Argentium, it will be annealed and very soft. Stick it in an oven for a few hours and it regains much of its hardness. It allows for thinner clips than if they were made in Sterling.
The germanium oxide layer does cause a few issues, one of which is a problem for me. It's not possible to reliably enamel over Argentium. I'll cover more of the details when I discuss enamels.
Just like Sterling, I usually buy Argentium in sheets, and casting grain. If I need wire or tube, I make it for that project.
Fine silver is defined as being at least 99.9% pure. It's inappropriate for most tasks as it's too soft. It does have the advantage of being a good metal to enamel. The only time I use fine silver is if I'll be enamelling the piece.
I occasionally buy fine silver as casting grain or sheet, however, most of my needs are served with custom made tube.
Gold is the ideal metal to work in for most projects. It is easy to solder, cast, make into wire or tube, and enamel. Unfortunately it's ridiculously expensive. When it is called for, I tend to use 18k yellow gold, and occasionally 18k white gold. To be assayed as 18k, it must contain at least 75% gold, with the balance made of silver, copper, or palladium, depending on the desired colour. Silver and copper are used for yellow gold, and silver and palladium for white.
I usually buy gold as casting grain.
Niello has been used since antiquity. It is defined as a sulphide of silver, copper, lead, or some combination of them. Traditionally it was made by alloying silver, copper and lead, and then pouring the molten alloy into sulphur. On top of making a nauseating cloud of smoke, the metal which comes out is a beautiful black colour. The advantage of niello over other techniques for blackening metal, such as liver of sulphur, the black goes through the metal. Most patinas will eventually rub off. Even if it is scratched, niello remains the same colour.
Once the niello has been made, it can be inlaid into engraved areas in the base piece. Traditionally it is used with gold, silver or bronze to provide contrast. I make my own niello using a few different recipes depending upon the properties I want (lower melting temperature, lower surface tension, harder, etc).
If you are interested in more technical information about niello, I have created a page where I will post more detailed information on its manufacture and use.
Enamel is one of those commonly used words which has been co-opted by various people marketing other materials. When speaking about jewellery, vitreous enamel is glass which has been mixed with various oxides and ground into a powder. The enamel powder is then fused onto a metal base at high temperatures (around 1450°F). During the firing process, oxides in the glass react with oxygen and the metal to change into the final colour. Many thin layers of enamel are required to achieve a fine finish. The process requires significant skill and time (enamelling a pen often doubles the time to make it).
Be wary of people passing off epoxies and acrylics as enamel. They look good initially, but tend to discolour over time. They also don't require very much time or skill to use, and shouldn't cost as much as a similar piece which has been enamelled.
The most effective use of enamel is over engine turning or guilloché. The surface of the metal is engine turned, and a translucent enamel is fused over top. The fine cuts of the engine turning and the coloured enamel produce a stunning surface which shimmers in the light.
The primary way to cast precious metals is the lost wax casting process. The process has been refined over millenia, however, it remains fundamentally the same. To begin with, a wax model of the piece is required. Traditionally bees wax, with some additives to make it harder, was used. Today we have access to a range of waxes in differing hardnesses. I use the hardest wax available so it will hold the fine details milled into it.
Once the wax model is made, a mould is made using high temperature investment plaster. The wax model is then melted out, exposing a cavity the molten metal can be poured into. Because the wax model is melted and destroyed, an original wax model is required for each piece cast.
Acrylic plastic is in wide spread use in the pen making. Compared with some of the early materials used by the pen industry, such as ebonite, bakelite, and celluloid, it comes in a wide range of colours, and is very stable. Despite what some manufacturers would have you believe, it is very inexpensive to produce. When paired with precious metals, it is a useful material to reduce the overall weight and cost of a pen.