The words that mean nothing.

Two factories can both say brushed and deliver surfaces that do not match under the same lamp. Neither is lying. The word describes a look, and a look is not a specification. The gap between the two surfaces is usually three variables: the last abrasive grade used, the direction the abrasive travelled, and whether a final hand pass was applied. All three can be written down.

The vocabulary, sorted

The trade uses five words for what is really a continuous scale.

Mirror, or polished. Successively finer abrasive passes ending in a soft mop with a fine compound. Reflective, the only finish where the surface shows geometry as a reflection.

Satin. A fine, even, usually non-directional haze. In many workshops this is produced by vibratory tumbling with a fine medium, which is why satin is often the cheapest uniform finish and why it has no grain direction.

Brushed. A linear grain, produced by an abrasive belt, a flap wheel or a scouring wheel. Directional by definition. Brushed with no direction named is an incomplete instruction.

Bead blast. A matte surface produced by propelling fine media at the metal. Uniform, non-directional, and it hides small scratches better than any other finish.

Tumbled. The mass-finishing step, producing anything from a satin to a near-mirror.

Satin in one workshop is brushed in another and tumbled in a third. The label is not portable; the process is.

What Ra measures

Ra is the arithmetic mean deviation of the surface profile from its mean line, expressed in micrometres. It is a single number for a texture, which is both its usefulness and its limitation.

Two cautions on the numbers. Ra does not capture direction: a hand-brushed surface and a machine-brushed one can share an Ra and look entirely different. And Ra does not capture regularity — a surface with a few deep scratches can measure acceptably and still be visually rejected. Measurement is by stylus profilometer on a flat sample, and most jewelry workshops do not own one, which is why the physical reference matters more than the figure.

Direction matters more than grit

On a flat tag, a linear grain running along the long axis reads as intentional, and the same grain running across it reads as a machining mark. On a ring or a bangle, the grain should run around the circumference: a linear grain applied across a curved band produces a surface that changes appearance as the piece rotates, and it looks like a defect even when it is uniform.

Three directions to name in a specification:

1. Linear, stated axis — along the length or across the width.
2. Circumferential — around a ring, bangle or cylinder.
3. Non-directional — vibratory or bead blast, uniform in all directions.

The coupon

The only reliable control is a physical reference agreed before production and retained by both sides.

A coupon of 50 × 50 mm, in the same alloy, finished to the intended standard, signed and dated. It costs almost nothing and it ends the argument that photographs cannot settle, because a photograph under a different light is not evidence. Ask for the coupon to be produced by the same sequence that will run the order, not polished by hand as a presentation piece.

Note also what finishing does to corrosion behaviour. Polishing can embed traces of free iron from contact with tooling, which is why a passivation step to ASTM A967 is worth specifying after heavy polishing, and why salt spray ranking to ASTM B117 or ISO 9227 is run on finished parts rather than bare coupons. Where a design carries a piercing post, EN 1811 nickel release testing applies to the finished part whatever the surface.

Coating changes the appearance

PVD is a conformal process: it adds roughly 0.5–1 µm and reproduces the substrate beneath it, texture and defects included. The same gold tone on a mirror and on a satin reads as two products — one a bright specular gold, one a soft matte gold — so the finish must be stated wherever a coated SKU is ordered. A coated layer is thin enough to telegraph a scratch or a polish drag rather than cover it, and compound left in a recess will outgas in the chamber and return as a localised blister; the control is a documented cleaning step between polishing and coating. The FTC's Jewelry Guides require finish descriptions not to mislead about how the surface was produced, so name the process; the Guides are published at 16 CFR Part 23.

What goes in the tech pack

Six lines for each finish on the piece:

1. Which faces — outside, inside, edges, recesses. Satin inside and mirror outside is often the correct answer on a bangle.
2. Which process — belt, mop, vibratory, blast.
3. Which abrasive grade or Ra — one or the other, stated.
4. Which direction — linear with the axis named, circumferential, or non-directional.
5. Which coating, and whether the finish is meant to be read under it.
6. The coupon reference — the approved sample, with its date.

Mirror typically takes three to five polishing stages with hand work in the recesses; satin takes one or two, and on a flat piece mirror can double the finishing labour. Buyers matching matte parts for charms or satin bracelets will find the mass-finishing route in how the piece gets made and how a coating reads the finish in PVD colour matching. To have a coupon produced and approved before the run, send the piece through the RFQ page.