Resources

Plating

  • Cleaning
    • Surgical cleanliness of all articles and equipment is very important. In all electroplating / colour gilding processes, it is essential that all surfaces to be covered are chemically clean. If a polished finish is required, it is important to ensure that the original surface to be plated /gilded is polished prior to plating, followed by electrolytic cleaning in a hot or cold alkaline cleaner, and where necessary, an acid dip should follow to remove tenacious oxide films. It is important to note that as little time as possible should elapse between cleaning and plating, since deposits on parts that spend long intervals between stages often do not have good adhesion or as bright appearance as those parts which pass uninterruptedly through the plating sequence. However, should there be any reason to delay its being placed in the plating solution, the object should be immersed in clean distilled water to prevent the formation of surface oxidization from air contamination.

      It is effective to check the quality of your cleaning before plating by doing a simple “water droplet test”. With your squeeze bottle drench the article with clean distilled water. If the water runs off in an even film the article has been cleaned properly. However, if the water disperses into droplets that cling to the article, this indicates the presence of grease or other foreign substances, and therefore should be cleaned again.

  • Electropolishing / Stripping Solution
    • This solution is cyanide-based and should therefore be handled with care. Wash hands thoroughly.

      Electropolishing / stripping is the process of anodical electrolytical removing or stripping, especially adherent solids, surface metal, surface oxide or old plating that must be removed before replating takes place. The process is the exact reverse of plating. The article here being the anode and the cathode of stainless steel. As in plating, it is essential that the article is perfectly clean and grease-free in order to obtain a good result. The chemical reaction involved generates considerable fumes and therefore a well ventilated work area or preferably a ventilation hood should be used. Likewise in plating, after electrostripping the entire surface of the object is left chemically clean.

      Procedure for Electropolishing: 

      With the crocodile clips, connect the red positive lead (anode) to the copper handling wire of the article, and the black negative lead to the stainless steel cathode. The stainless steel cathode should be immersed up to at least 10cm and the article immersed completely.

      If the electropolishing / stripping solution is used at high temperatures and voltages (±80°c / ±6 to 15 volts) *it acts as a stripping solution and is very effective in the removal of projections or rough surfaces which frequently appear on castings.

      If used at low temperature and voltages (±40°c / ±3 to 6 volts) *it acts more as a polishing solution in refining the surface of the object.

      *It is up to you as the individual plater to decide which temperature and voltage suits you and your style of work best. To come to that conclusion may mean having to “play” around with the solution at different temperatures and voltages using a spare piece of work to realize the optimum conditions specific to your needs.

      The stripping action should be watched carefully as once the surface metal is stripped, the base metal will be attacked and etched, which may not be desirable. Periodic reversal of the current is sometimes employed to keep the surface smooth.

      Please note: The above temperatures and voltages are guidelines only!

  • Buffing and Polishing
    • Buffing and polishing are important steps to quality plating because scratches, imperfections and discolouration are never hidden by the plating and must therefore be removed at this stage. When polishing, remember that a light pressure on the buff or circular brush is sufficient to obtain a good result.

      Silver is the softest of the precious metals and hence care must be taken when buffing as burns can easily occur. Avoid heavy pressure on the buff, and always use a light polishing compound.

  • Masking
    • By means of a masking lacquer, we offer you the possibility of doing two-tone work. Simply cover the part of the article which is to remain the original colour (which you may or may not have previously plated) with the masking lacquer, not forgetting to leave a small section free of the lacquer to which the handling wire is to be attached for the electrical connection. This is because the masking lacquer acts as an insulator. After plating, the lacquer can be removed by rinsing in acetone and a wash-out brush. Finally, rinse in water.

  • Gold Plating
    • The high resistance of gold to corrosion and its complete freedom from atmospheric attack has lead to its steadily increasing use over the past decade. Its properties as an electrodeposited light-duty contact material offer advantages over most other metals.

      Pre-Treatment:
      For successful plating it is important to ensure that the surface on which the metal is to be deposited is chemically clean.
      It is unusual to electrodeposit gold into an undercoat of silver, although it is claimed that for a thin gold deposit, an undercoat of nickel is preferable. It is recommended that article for gold plating be degreased and then treated in an alkaline cleaner, followed by a thin deposit of copper before silver or nickel plating. If a polished finish is required, it is essential that the original surface to be plated is polished before plating takes place.

      Operating the bath:
      Conventional gold plating solutions should be used at a temperature of 60°c with a current density of between 1.5 and 3 amps sq. ft. (0.167- 0.333 A/dm).

      Anode: 
      In gold plating by cyanide process, a soluble anode (fine gold) is generally used, although an insoluble anode such as platinised titanium may used. The used of gold anodes ensure that the amount of metal in the plating solution remains reasonable steady for longer periods. With an insoluble anode (Pt/Ti) the electrodeposited gold is derived entirely from the electrolyte.

      With gold anodes, the cathode efficiency is always 100% and the balance of the gold content in the bath is maintained.

  • Silver Plating
    • High conductivity, good chemical resistance and good solderability make silver an ideal contact material. The metal is not subject to oxidization at ordinary temperature. As in all electroplating processes it is essential that the surface to be covered is chemically clean.
      It is important to remember that as little time as possible should elapse between cleaning and plating, since deposits on parts that spend long intervals between stages often do not have as good adhesion and bright appearance as those parts which pass uninterruptedly through the plating sequence.

      Silver can be plated directly onto copper and brass.
      This solution will produce a mirror bright silver deposit on polished or plated substrates. The throwing power is excellent, enabling deep drawn contacts and components to be completely coated. The solution is to be operated at a temperature ranging between 20 and 30°c. The voltage should be between 1 and 2 volts.

      The anode/cathode ratio should be least 1 to 1. The anode should be of fine silver annealed (99.97% purity), and should be enclosed in a nylon anode bag. Agitation by rod movement.

  • Silver Oxidising Solution
    • This solution is for silver or silver plated articles.
      For silver plated articles, the deposit of silver must be of sufficient thickness to withstand the chemical reaction of the “oxidizing” solution. Usually, deposition for half an hour at 0.3 to 0.4 amps/dm is sufficient for plain articles. Scroll or filigree work must be given longer.

      Use silver oxidizing solution at a temperature of around 65°c.
      While immersed, the article must be kept moving. After 10 to 20 seconds the article will become dark slate in colour and should be removed. Rinse in cold water.

      For a uniform finish, make sure the article is clean before immersing in the solution.

  • Rhodium Pen / Brush Plating
    • Pen / brush plating can be useful when plating is only required on localised areas of a piece of the work without the need to immerse the object into a plating bath.

      Its function can also be to repair plated areas that have been worn away.

      Equipment:
      Minimal equipment is required. The power source to be used is a DC rectifier with an ammeter to measure the current and to control the plating thickness. The pen is attached to the anode or positive pole and the object is attached to the cathode or negative pole.

      The nib of the pen should be absorbent (felt/cotton) to create a good electrical conductor and to spread the metal solution efficiently. The nib should be kept spotlessly clean so as not to contaminate the solution to be used. It is very important to keep all equipment clinically clean to reap the benefits of a high quality of plating.

      Preparation:
      Bear in mind that not only the surface to be plated, but the entire object should be absolutely clean. Try the “water droplet test” to ensure the surface is chemically clean and if it fails the article is to be cleaned again.

      If only a small specific area of the article is to be plated, it is normally a good idea to mask off the area not needing to be plated with masking paint.
      This will ensure accuracy of plating and ultimately a more professional finished piece.

      Plating:
      Pen plating solution is far more concentrated than solutions prepared for use in plating tanks, and therefore comes in smaller quantities.

      Small amounts of solution to be used must be decanted from the stock container, never to be returned for fear of contamination of the entire contents. It is therefore important to decant only small amounts of solution anticipated as sufficient for immediate use into an open glass container. Always keep the stock container tightly closed.

      Attach the piece to be plated to the cathode on your power source and the plating pen/brush to the anode. The voltage to be used is slightly higher than that used in a plating bath. The plater will have to determine optimums specific to his / her needs.

      Immerse the plating nib into the prepared solution for about 5 seconds. Apply parallel strokes at the rate of about one per second, systematically brush the surface in the lengthwise direction of the area, or use a circular motion and cover the entire area with overlapping strokes. Work for about 25 seconds at a time, then immerse the nib into the solution for about 5 seconds and repeat the process.

      Visually monitor the metal deposit, if it appears dull or becomes black, decrease the voltage or increase the brush stroke speed. Continue applications until a plate of desired thickness is achieved.

      Switch off the power source, disconnect the work, rinse well under running water and dry with a clean dry cloth.

  • Rhodium Bath Plating
    • Rhodium electrodeposits have been used in the jewellery trade for many years as a method of protecting silver from tarnish, and in the setting of diamonds.

      Articles that can be directly rhodium plated must be carefully prepared for plating, since good adhesion of rhodium to the basis metal can only be obtained on nickel, silver, gold, copper, brass, bronze and platinum. Because of its acid content, rhodium cannot be deposited directly into steel, iron, zinc, aluminium, lead and tin.

      Therefore a preliminary deposit of silver is normally needed.

      Procedure:
      If a polished finish is required, it is necessary to polish the base material and then the undercoat is applied.

      This solution should be used at a temperature of between 20 and 50°c with a low voltage of between 1 and 2 volts. Higher voltages may result in burning.

      The rhodium electrolyte has a high sulphuric acid content and it may attack areas of the metal ions. It is essential that the rhodium solution be kept free from suspended solids.

      To prevent contamination, the bath should be sited in a clean environment, and the tank should be covered when not in use.

      Anode: Rhodium plating is an insoluble process for which platinum titanium anodes can be used.   The surface area is not critical.

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