Rose Gold, Rhodium, Gold | Plating Demystified (and more)
You may have heard of gold plating, but what exactly is it? And why is it used in jewelry making? Here, I hope to demystify it and show you the tools and equipment needed to plate your own items quickly and easily.
So, what is plating? The correct term for the process is “Electroplating”. A liquid is used, which contains the precious metal dissolved within a chemical solution. Electricity is used to transfer the precious metal out of the chemical solution and bond it to the item of jewelry.
Gold plating is a simple way to add value to non-precious metal pieces by adding a layer of gold. Hence the piece will have the appearance of gold but can be made from a much cheaper metal. This process is often used on base metal ‘costume’ jewelry. Gold plating is also used on electrical connectors and contacts as an anti-corrosion and conductive treatment. Some jewelry manufacturers even gold plate over gold items. This is to improve the surface finish and cover up any discoloration or other marks such as soldering.
Many people refer to items of jewelry as being silver plated. In most cases, this is not correct. A more common process is to use “Rhodium plating”. Rhodium is a bright white precious metal, similar to platinum. Plating in Rhodium gives a very bright highly reflective surface. This is often used on sterling silver items to improve the brightness of the finish and to avoid tarnishing. Due to its bright finish, rhodium plating is also used on claw settings and mounts of gemstone rings as it helps to reflect the light around diamonds and add sparkle.
Likewise, “white gold” items such as rings are often Rhodium plated, again to improve their brightness. However, when such rings are nested together, they will rub and can wear down the thin plating. Jewelers therefore recommend that white gold rings are re-plated annually to keep their bright luster. This can be done very simply in a matter of seconds.
Non-precious metals such as zinc, copper, and nickel are also commonly used in electroplating. They can be used on their own as anti-corrosion treatments, or in jewelry making copper and nickel are sometimes used as surface treatments, prior to gold and rhodium plating.
Rather like painting a wooden fence, the application of a base coat can have many advantages. Copper or copper mixed in gold alloys or sterling silver can tend to leech into the plated surface, and subsequently oxidize. This means that an item that has been gold plated could still tarnish, as the plated surface becomes contaminated by the underlying copper. One solution to this is to pre-plate with a layer of nickel. This nickel layer acts as a “barrier”. To prevent the copper atoms from moving into the gold layer. It also helps to provide a smooth semi-reflective surface, which all help to create a better final finish on the gold-plated layer.
Above. Nickel barrier layer, before applying the top gold layer.
On a commercial scale, base metal costume jewelry is often plated in several layers, starting with copper to form a base and a key, then nickel to act as a barrier, and finally gold or rhodium to create a bright finish.
Base metal, Copper, Nickel, Rhodium
How is it done?
Despite the complex science, electroplating as a very quick and simple process. In most cases taking only a few seconds. The prerequisites are a plating solution and a device that can provide an electrical current. Pepetools make several plating units for big and small jobs, aimed at the jewelry market. Depending on the scale and amount you wish to plate, here are a few considerations.
The first thing you’ll need is the plating solution itself. Either in liquid form or as dry salts which are mixed with distilled water. It is important that you get the right solution. Some solutions are designed to be used in immersion plating units. I.e. small baths, (jars or beakers) for plating bangles, bracelets and larger items where the item is “immersed” in the solution. Pen plating systems allow the solution to be painted onto the jewelry (discussed later). These require more concentrated solutions. So, it’s important to get the right one either for pen plating or for immersion (bath) plating.
Power to the people.
The next thing you need is a power supply, known as a rectifier. This produces the electrical current needed. Pepetools offer several models that vary in power. The manufacturers of the plating solution will specify the current needed to plate a certain surface area. Typically, this is specified in amps required to plate a square decimeter. That’s 10cm X 10cm or 100cm2 (about 15 ½ square inches). For example, if the solution specifies 1 Amp per square decimeter, then a 25 Amp rectifier would, in theory, be able to plate 25 square decimeters in one go (a little over 2½ Square feet). Remembering of course that an item such as flat sheet would have two sides, and hence twice the surface area.
Above, The Pepetools Programmable 60 Amp Digital Rectifier
In practical terms, for the small jewelry shop, 10 Amps is sufficient. You will notice that the Pepetools units offer much higher power such as 25A, for a marginal price difference. For this reason, a 25A unit will usually offer the best value. Whilst jewelry tends to be all a similar size, the more powerful units give the opportunity to plate multiple pieces at the same time. This is great for small production runs, or for busy shops where multiple items can be immersed and plated at the same time, in a single dip. Ultimately saving time, saving money and making the most efficient use of valuable materials.
Above. Pepetools 25 Amp PLating Rectifier
Always follow the specific instructions, but typically the rectifier connects to the anode (metal strip), which is placed in the solution. The cathode is attached to the jewelry via a clip or piece of copper wire, which is then suspended in the solution. As the current is applied the electricity flows through the liquid and to the jewelry, depositing the gold, out of the solution and bonding it onto the jewelry.
In theory, it is possible to place the jewelry straight into the gold plating solution. But grease, dirt, and contaminants can give a poor result. So, for this reason, it is common to use several beakers (baths) for cleaning and preparing the jewelry before plating.
Distilled water is used to rinse and clean the jewelry as it leaves no mineral deposits or contamination (which normal faucet water may do). The piece to be plated will be rinsed before dipping in each solution, to remove previous chemicals and avoid any cross-contamination of the solutions.
Stage 1 Cleaning
Cleaning salts are also used. Typically, a salt such as sodium hydroxide is dissolved in warm water to make a conductive solution. The jewelry is placed in this salt bath (with power) and the current forms bubbles on the surface which helps to clean the piece. Typically, just a few seconds is all that is required.
Stage 2 Surface Prep
The second stage will depend on the final plating being used, and the manufacturers' instructions. But this second stage can be an acid bath, to etch the surface, This is particularly useful when re-plating items such as white gold rings, as the acid helps to provide a key, for the new layer.
Alternatively, as mentioned before. This second bath can be used for pre-plating such as a nickel layer to seal the jewelry.
Stage 3 plating.
Once cleaned and rinsed the jewelry can then be immersed in the gold plating solution. It is important that the voltage and power are set to that required by the solution. It is important to read the advice on all salts and solutions. It should be obvious then the piece is plated. Usually, this will only take a few seconds.
The piece is then again rinsed. Dried and is ready for wear.
Above. The Pepetools digital pen plating station.
control unit with three pots, clip and pen
Pen plating is a quick and easy way to plate small items. Instead of immersing the whole piece. The solution is applied using a felt pen, which is in turn connected to the power supply. The gold can effectively be drawn onto the piece, very selectively and accurately. This allows the highlighting of certain parts to create contrast. E.g. gold plating the bud of a silver flower. This is also immensely useful when rhodium plating gem-set yellow gold rings. Using a pen plater, it is possible to apply rhodium to just the mount, without the need for masking or protecting the yellow parts of the ring.
Top tip !
Pen platers do not use beakers or baths, the pen is simply used to add the gold or rhodium plated. As there is no salt cleaning stage, it is vital that the piece is cleaned thoroughly and is free from any grease. Degreaser such as acetone or alcohol can be used to clean, rinse in distilled water prior to plating.
Above. Applying gold plating to a silver flower,
using the Pepetools Digital Pen plating Station.
The piece to be plated is attached to the crocodile clip (cathode). The felt pen represents the anode. But instead of being immersed in the solution, the felt tip is dipped into the solution and then applied directly to the piece. The pen plater provides a current between the pen nib and the piece. The gold is drawn out of the plating solution held within the nib and bonded onto the piece. The gold is “painted” onto the piece using the pen. Occasionally refresh the felt tip in the solution, when it is no longer plating. Once plated the piece can be rinsed in water and dried. It is now ready to wear.
So, whilst the art of gold plating may seem complex, it is very simple taking only a few seconds. Requiring little more than immersing the piece in a beaker or brushing it with a felt pen.
Tips on plating.
In all cases, the piece must be clean a grease-free. Even grease from your fingers can cause a barrier to plating solutions. So, clean the piece thoroughly, either using alcohol or by using a salt bath. Once cleaned avoid touching the piece with bare fingers.
It is possible to mask areas you do not wish to plate by using anything waterproof. Plastic tape can be used to cover areas. Etch resistant pens (as used in electronics) can also be used. Alternatives include nail polish, which can be removed later using acetone. The pen plater is ideal for small precise plating and the felt tips can even be shaped with a craft knife to give maximum precision.
The plated layer is very thin, only a few molecules. So, whilst it can improve the surface of an item, it cannot fill deep scratches, dents or physical imperfections. For this reason, it is important to finish the piece completely prior to plating. If a shiny finish is required, then the piece should be fully mirror polished first and thoroughly cleaned before gold or rhodium plating. Excessive polishing and buffing afterward could remove the plating.
Hammered textured finishes.
Likewise, if a texture is required this must be applied first, and only when complete and cleaned should it then be plated.
When done correctly, this plated layer is permanent. It should not flake or peel off. However, the plated layer is very thin. So, the plated surface can be prone to wear and tear, if constantly rubbed. Items such as nested rings or moving pendants on a chain can wear very quickly and may re-planting annually, depending on wear.
The solutions used are usually strongly acidic or Alkaline and so sensible precautions should be observed. Gloves should always be worn and the process carried out in a safe, well-ventilated area. All chemicals should be kept away from pets and children. In all cases, it is vital to follow manufacturers' instructions for both the plating units and the chemicals used.
The information given here is just a general overview of the processes and terminology surrounding plating. I hope I have helped to demystify it a little. With a simple set up and few chemicals, you can easily create your own plated items quickly and easily. For more information check out Pepetools range of platers and rectifiers.
Written and illustrated by Dave Wilson