A superficial proposition:

Professionals and clients have a right to know the roughness of the surface finish of body jewelry from each manufacturer they choose to do business with. Roughness can be measured as R_a to the microinch (µin) or Metric: micrometer (µ) or nanometer (nm). (The final smooth finish for many polished surgical implants is specified at 0.025µm to 0.05µm (1µin to 2µin)). This would alleviate confusion and allow a more frank discussion of the merits of different processes to arrive at a desired finish.

Smoother is better in our case, but how smooth is smooth enough?

1. The body jewelry industry should establish an acceptable minimum standard for surface finish and passivation based on current science.
   1. I propose we aim for a R_a minimum of 1µin to 2µin or smoother for initial jewelry for healing rather than the subjective term “mirror finish”.
      Random testing of jewelry samples from Anatometal, Industrial Strength and NeoMetal have shown this to be possible, and samples from Glasswear Studios and Gorilla Glass have shown that it can be exceeded with surfaces approaching <0.5µin.
   2. Jewelry manufacturers should help us understand what is achievable with their current practices.
2. Jewelry manufacturers should specify the goal surface finish measurements of their body jewelry in S_a or RR_q or R_RMS 

Why does it matter?

A smoother surface adheres less to tissue during healing, and allows less bacterial colonization and inhibits corrosion. A lower Roughness measurement means a smoother and more regular surface (1µin to 2µin or better should be the goal)

“Mirror finish” seems subjective, so we attempt to address this

Our colleagues have long referred to the goal appearance of a polished surface for body jewelry as a “mirror finish” to indicate that a layperson could see their reflection. Our goal is to provide a professional comprehension of the superficial characteristics of roughness which influence healing and scar formation.

How can I measure the surface finish of my jewelry?

A good magnifying loupe or microscope will help demonstrate the difference in some surface finishes to a lay person or customers, or at least photos taken with decent lighting and a quality macro photo lens, but a non-contact profilometer is required to take an accurate scientific measurement of body jewelry.

• I’m really interested in what manufacturers QA can propose, as the goal of the polishing process depends on the method and the skill of the worker when it comes to hand polish.
• I believe that a manufacturer should check the R_a frequently between batches, then establish what they consider an acceptable R_a and state publicly that they aim for a certain smoothness.
• I would love to participate in a blind analysis of jewelry quality! We can get a third party lab to do the tests, and get contributions to cover it. Raquel and Jeff Martin and I proposed that in 1996, and started an APP committee, collected samples and eventually tested a few. It is past time to follow up with the jewelry review committee. Rob Hill from Prysm body piercing has done useful tests for his APP Scratching the Surface presentation.

Applicable references for standards of surface finishing:

• ISO 1302
• ASTM F2791
• ASTM F86

10. Techniques for Surface Texture Measurement
10.1 Surface profiles can be measured using both contact and non-contact methods. The former approach involves tracing the surface profile with a stylus that is in contact with the surface; a method unsuitable for materials that are soft or easily damaged. Non-contact methods are better suited to these materials. Non-contact methods include vertical scanning white light interferometers and confocal microscopes (2, 3, 4).

— Quote from ASTM F2791

Table from ISO 1302: Surface texture measurements

Roughness values Ra	Roughness values Ra	Roughness
micrometers	microinches	Grade Numbers
50	2000	N12
25	1000	N11
12.5	500	N10
6.3	250	N9
3.2	125	N8
1.6	63	N7
0.8	32	N6
0.4	16	N5
0.2	8	N4
0.1	4	N3
0.05	2	N2
0.025	1	N1

In finish milling operations typical surface roughness levels vary from N6 to N9.

—Surface roughness monitoring application based on artificial neural networks for ball end milling operations:

Surface roughness is the measure if the finer surface irregularities in the surface texture. These are the result of the manufacturing process employed to create the surface. Surface roughness Ra is rated as the arithmetic average deviation of the surface valleys and peaks expressed in micro inches or micro meters. ISO standards use the term CLA (Center Line Average). Both are interpreted identical.

The ability of a manufacturing operation to produce a specific surface roughness depends on many factors. For example, in end mill cutting, the final surface depends on the rotational speed of the end mill cutter, the velocity of the traverse, the rate of feed, the amount and type of lubrication at the point of cutting, and the mechanical properties of the piece being machined. A small change in any of the above factors can have a significant effect on the surface produced.
—From the Engineer’s Edge:

SURFACE ROUGHNESS AVERAGE OBTAINABLE BY COMMON PRODUCTION METHODS

 

Table 1: Comparison of surface finish obtainable by different finishing processes

S.No.	Finishing Process	Workpiece	Ra Value (nm)
1	Grinding	–	25 – 6250
2	Honing	–	25 – 1500
3	Lapping	–	13 – 750
4	Abrasive flow Machining (AFM) With SiC abrasives	Hardened Steel	50
5	Magnetic Abrasive finishing (MAF)	Stainless steel	7.6
6	Magnetic Float Polishing (MFP) with CeO2	Si3N4	4.0
7	Magnetorheological Finishing (MRF) with CeO2	Flat BK7 Glass	0.8
8	Elastic Emission Machining (EEM) with ZrO2 abrasives	Silicon	<0.5
9	Ion Beam Machining (IBM)	Cemented Carbide	0.1

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Further resources

— Antibacterial Surface Treatment for Orthopaedic Implants
https://www.mdpi.com/1422-0067/15/8/13849/htm

Read more about foreign body response and fibrotic capsule formation for intradermal implants