When you think of gold you may think of glamor, allure, enchantment. Gold contains a variety of unique properties that make it ideally suited for a wide array of plating processes – including a significant value from an electroplating perspective. You may wonder why should gold be plated rather than using pure gold components or base materials? 

Gold plating, otherwise known as gold electroplating, is a process in which a thin coating or layer of gold is placed onto the surface of a metallic object. The method involves electrodeposition. Electrodeposition is when an electric current is passed through a liquid electrolyte compound present with dissolved gold ions along with other chemicals. Subsequently, the ions adhere to the surface of the subject which result in the beautiful formation of the protective gold layer. 

While plating gold can be more costly in comparison to other materials, this lustrous metal bestows a number of advantages in a wide variety of metal finishing applications. Generally speaking, if the additional upfront cost of utilizing the option of gold plating, it is most often the greatest plating option. 

While gold plating is attractive to the eye, there are also a number of benefits this process entails including:

Corrosion prevention: The least reactive of all metals, gold coating will enhance the subject’s ability to resist corrosion as well as increase the subject’s longevity 

Promotion of electrical conductivity: It is less commonly known that gold has a natural ability to conduct electricity making it an ideal conductor for various electrical manufacturing applications

An increase in wear resistance: Gold enhances an object’s longevity by increasing its protection from wear and tear. This is especially helpful in  heavy-use conditions.

Extreme heat protection: Gold plating can serve as a heat protector that will safe-guard the subject from potential damage caused by elevated temperature vulnerability. 


  • Type I: A, B or C
  • Type II: B, C or D
  • Type III: A only
  • Hard Gold
  • Soft Gold


  • Barrel Plating 
  • Rack Plating 
  • Vibratory Plating 


In some scenarios, it may be necessary to perform gold plating to meet engineering or military specifications.




The MIL-DTL-45204D gold plating spec satisfies the criteria for the U.S. Department of Defense, its various support agencies, and supersedes the previous MIL-G-45204C caliber. This spec classifies gold type based on the purity of the substance: Type I comprises a minimum gold content of 99.7 percent, Type II consists of 99.0 percent and Type III includes  99.9 percent. Correspondingly, there are four hardness grades based on the Knoop scale: Grade A (90 max.), Grade B (91-129), Grade C (139-200) and Grade D (201 and over).

Possible combinations for purity vs. hardness include the following:

  • Type I: A, B or C
  • Type II: B, C or D
  • Type III: A

Additionally, there are gold plating thickness standards under this military spec. Listed below are eight classes corresponding to the acceptable minimum thickness:

  • Class 00-0.00002
  • Class 0-0.00003
  • Class 1-0.00005
  • Class 2-0.00010
  • Class 3-0.00020
  • Class 4-0.00030
  • Class 5-0.00050
  • Class 6-0.00150

Furthermore, there are fixed requirements for the underplating of gold coating. Based on the application and environment, an undercoating of nickel, copper or a Cu/Ni may be utilized to fulfill the contract requirements. It is recommended that you avoid using a silver or silver/copper underplate unless specifically required for the project. Regardless of the composition of the underplating, it is necessary to apply a soft gold strike atop the undercoating prior to the addition of the final coating of gold to promote adhesion and reduce the risk of contamination.


The ASTM B488 gold plating standard appeals to engineering applications. Gold coatings that comply with this spec most frequently are utilized to increase the substrate’s resistance to corrosion as well as to prevent tarnishing. The classes and types under this specification reflect those of the MIL-DTL-45204D gold plating standard. However, there are some distinctions in the thickness requirements. The seven thickness classes under ASTM B488 gold plating involve:

  • 0.25-0.25 um
  • 0.50-0.50 um
  • 0.75-0.75 um
  • 1.0-1.0 um
  • 1.25-1.25 un
  • 2.5-2.5 um
  • 5-5.0 um

Nickel is typically the preferred choice when it comes to underplating. However, applications which require coating with a thickness that exceeds 5.0 um with copper or copper alloy substrates are the exception. Another reason nickel is popular as an undercoat is its brightening ability for the leveling layer. It can act as a corrosion protector in the surface pores which prevents tarnish on the gold topcoat. Nickel serves as a support bearing underlayer for the contacting exteriors. 

The complication of this standard initiates an ASTM Type designation that is new requiring purity, which is set up for electrodeposited gold:

  • Mass percent gold, minimum, without the presence of potassium, carbon as well as nitrogen 99.70: New ASTM Type I, MIL-DTL-45204 Type I, Old ASTM Type 2
  • Mass percent gold, minimum, without the presence of potassium, carbon as well as nitrogen 99.00: New ASTM Type II, MIL-DTL-45204 Type II, Old ASTM Type 3
  • Mass percent gold, minimum, without the presence of potassium, carbon as well as nitrogen 99.90: New ASTM Type III, MIL-DTL-45204 Type III, Old ASTM Type 1

The hardness values are defined by ASTM Code:

  • Knoop Hardness Range 90 HK25 maximum: ASTM Code A
  • Knoop Hardness Range 91–129 HK25: ASTM Code B
  • Knoop Hardness Range 130–200 HK25: ASTM Code C
  • Knoop Hardness Range >200 HK25: ASTM Code D

When it comes to the relationship between purity and hardness for excellent commercial practice, the following combinations are fully representative:

  • New ASTM I – Old ASTM Type 2 – Code A, B and C
  • New ASTM II – Old ASTM Type 3 – Code B, C and D
  • New ASTM III – Old ASTM 1 – Code A 

Aerospace Metals is proud to offer its gold plating capabilities and competitively quick turnaround time. If you’d like to learn more about gold plating or any of our other capabilities please give us a call at 800.398.0790 or send us an email info@aerospacemetalsllc.com. We would be happy to provide you with a free quote and samples.