Gold electroplating is the process of depositing a very thin gold layer onto the surface of another metal. The process has many uses such as in jewelry and the semiconductor industry. Gold plating is important in electronics, as it makes the surface of electronic components corrosion-resistant.

Creating a Gold Plating Emulsion

(Pixabay / sferrario1968)

Gold plating uses an alkaline gold plating solution to deposit gold onto a metal substrate by electrolysis. Following the old tradition, the gold plating solution used cyanide compounds, which are poisonous and must be dispensed in a very restrictive manner. Gold plating can now be executed with the use of publicly available chemicals, which are not as toxic as the cyanide compounds but can still be poisonous.

Here are the steps for preparing the gold plating compound:

  • Prepare the acid – This step may be skipped if you already have nitric acid with a concentration of 50% or higher. Gold may be dissolved using aqua regia or royal water, which is nitric acid, combined with hydrochloric acid at a ratio of 1:3. Hydrochloric acid is commercially available as muriatic acid. Nitric acid is restricted and must be prepared using available chemicals. One way of preparing nitric acid is by catalyzing a reaction of sodium nitrate with sulphuric acid and distilling the mixture to reduce acid to a concentration higher than 90%. At 90% concentration, nitric acid becomes highly corrosive and will produce fumes of toxic nitrogen dioxide gas.
  • Make the gold chloride – Gold chloride can be made by dissolving gold in aqua regia. The reaction of these two components produces toxic fumes, so the process is conducted under a fume hood or outdoors. Gold will dissolve in around 20 minutes at room temperature. The result of the reaction will be a solution of dissolved gold, copper compounds, and solid crystals of silver salts. Filtration will separate the liquid from the solids. Gold will then be precipitated out of the solution by adding a sodium metabisulfite solution. The final step will be the separation of the solid gold to be dissolved again in aqua regia. The acid needs to be evaporated at 120°C to obtain the red gold chloride crystals.
  • Create the gold plating mixture – For this step, prepare a strong alkaline solution of gold chloride and potassium ferrocyanide. The solution and the electric current will allow gold to be deposited over the surface of another metal.

Gold plating is not for novices. The process should be executed with great caution.