Where the
world gathers for metal finishing
Q&As since 1989


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Gold is too shiny: what do I do?

Is there any industry-accepted definition of shininess? Is there an instrument that measures it? Is there a way to control it in plating gold over nickel over copper on printed circuit laminate? I am not referring to pure reflectivity. I am referring to the capacity of the surface to disperse or diffuse the incident light: its ability to act like flat white paper versus its capacity to act like a mirror. Terminology might include specularity, nebulosity, gloss, dullness, mattitude.

The problem is I am getting surfaces that are TOO shiny, and I want surfaces that reflect just as much light, but are less mirrorlike. Thanks in advance.

Doug Raymond
Walnut Creek, Calif. USA
1998

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I guess I don't quite understand the difference between being mirror like and being reflective. However, in the plating industry I think shininess is usually quanitified as a surface finish or surface texture requirement. Read specification ASME B46.1 for the definition of surface texture used often in the plating industry. This surface texture is recorded in root mean square (rms) micro-inches. And in general as you go lower in micro-inches the surface becomes more reflective and shiny. For example, a surface of 35 micro-inches appears to be somewhat dull, while a surface finish of 5 micro-inches appears to be quite shiny.

In plating you can very the shininess (or dullness)of plating by varying the concentration of chemicals in the bath or by changing current density. I have not worked specifically with gold plating but I have worked with cyanide copper, silver, and cadmium plating baths. The surface finish or dullness can be varied in these baths by changing cyanide to metal ratios or by adding (or removing) organic brightening agents. Proper experimentation with a Hull Cell tester can give you the best chemical composition of your plating bath.

Also final surface properties will depend largely on prior finishing (grinding, polishing).

There are instruments available to measure the surface finish. Surface mapping equipment is available to be used with PC based programs.

Finally, can you give me any more practical examples of the difference betweeen shininess and reflectivity. I would like to learn more about this subject.

Greg Haataja
helicopters - Fort Worth, Texas
1998

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1998

Doug,

What you are looking for is more diffuse reflectance from the surface. This is controlled by the surface riughness. The solar energy people have developed techniques for measuring the spectral and diffuse reflectance. Suggest that you look in the journal - Solar Materials.

Donald M. Mattox
Society of Vacuum Coaters
Albuquerque, New Mexico

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A reference: The Surface Condition and Reflectivity of Metals. by JH Nelson, Journal of the Electrodepositors' Technical Society, Volume XXI, 1945-46, pp 113-119.

  
Tom Pullizzi
Falls Township, Pennsylvania