How to Specify a Brushed Finish on an Audio Front Panel

August 28, 2026

A brushed panel is the most common finish in hi-fi and one of the least well specified. “Brushed aluminum” on a drawing is roughly as useful as “painted”. The result depends on grit, direction, pressure, equipment and the operator, and none of those are in the words.

What brushing actually is

A brush finish is a controlled, directional abrasion of the surface. It is produced with an abrasive belt, a Scotch-Brite style non-woven wheel, a wire wheel or a dedicated brushing machine with a rotating drum, while the part passes underneath on a conveyor or a fixture.

The result is a set of fine parallel scratches. Because they all run the same way, light reflects along the grain and the surface reads as satin rather than as damage.

Two things follow from that:

It is subtractive. Brushing removes material, typically a few microns, and it removes it unevenly. On a part with a tight thickness tolerance, say so before brushing is planned.
It is directional. Turn the part ninety degrees and it looks like a different colour.

The specification that works

Put all five of these on the drawing:

Process: mechanical brush, or non-woven abrasive, or wire brush. These do not look alike.
Grit or equivalent: for example 240 grit, or Scotch-Brite very fine. A grit number on its own is meaningful only for belts.
Direction: with an arrow on the drawing view. “Grain parallel to the long edge” and an arrow. Never leave it to be inferred.
Which faces: front face only, or front face plus the top chamfer, and what happens on the ends.
Reference sample: the only thing that closes the gap between a number and an appearance.

A drawing note that does the job:

FINISH: MECHANICAL BRUSH, 240 GRIT EQUIVALENT, UNIFORM SATIN
GRAIN PARALLEL TO LONG EDGE, SEE ARROW
BRUSH FRONT FACE AND TOP CHAMFER ONLY
THEN ANODIZE PER MIL-A-8625 TYPE II CLASS 2 BLACK, 10-15 MICRONS
APPEARANCE TO MATCH APPROVED SAMPLE

Grain continuity across parts

This is the detail that separates products that look designed from products that look assembled.

If a front panel sits next to a side cheek, and both are brushed, the grain either lines up or it does not. When it does not, the eye reads the seam immediately even if the gap is perfect.

Options:

Run the grain the same way on both and accept that the two surfaces are still separate. This is the normal answer.
Brush the two parts together on one fixture, so the grain is physically continuous. Expensive, occasionally worth it on a flagship product.
Break the relationship deliberately: run the grain vertically on one and horizontally on the other, so the eye reads it as a design choice instead of a mismatch.

Whichever you pick, it belongs on the drawing of both parts.

Dry brushing, wet brushing and gloss

Shops differ in method and it changes the result.

Dry brushing with abrasive belts gives a crisper, more open grain. Common in European finishing shops.
Brushing with oil or coolant produces a smoother, glossier, more closed grain. Common in Asian shops and often what buyers mean when they say they want it to look like a Japanese amplifier from the 1980s.

Neither is correct in the abstract. If you have a reference part you like, the shop can usually tell from it which route was used. Send the part.

What brushing does not fix

Brushing is often sold as a way to hide machining. It only partly is.

Fine tool paths on a flat face: brushing hides them well.
A deep witness mark or a step between two passes: brushing does not hide it. It has to be machined out or sanded out first.
Chatter: brushing makes it worse, because the grain lights up the periodic pattern.
Alloy structure and grain from the mill: on some plate the material’s own rolling structure is visible after brushing and anodizing. It looks like a faint cloudy streaking that follows no tool path. Bead blasting before brushing reduces it.

If the part must be flawless, the sequence is machine, sand or blast to remove machining evidence, then brush.

Handling after brushing

A brushed, unanodized part is at its most vulnerable. The surface is clean, open and soft, and a fingerprint at that point can etch into the anodize later as a visible mark.

Ask the shop for:

Gloves from brushing onward
Parts kept separated, never stacked face to face
Minimum time between brushing and anodizing
Protective film only after anodizing, not before, since adhesive on a pre-anodize surface causes its own marks

Inspection

Judge a brushed panel the way a customer will:

Diffuse light, not a spotlight. A spotlight flatters and hides.
At arm’s length first, then at 300 mm.
Rotate it. Directional finishes change completely with viewing angle.
Against the reference sample, physically side by side.
On the whole set, not one part.

Write down the light and the distance in the inspection note. “Inspected under D65 diffuse light at 500 mm” is a standard. “Looks good” is not.

Frequently asked questions

What grit should I ask for?

For a front panel, somewhere between 180 and 320 covers almost everything. 180 gives a coarse, visible grain that reads as industrial. 320 gives a fine satin that reads as expensive. Ask the shop for samples at two or three grits on your alloy before you choose, because the number alone does not tell you what it looks like.

Can the shop brush after anodizing?

No. Brushing removes the anodize layer. The order is always machine, deburr, brush, clean, anodize. If a part needs rework on the finish after anodizing, it has to be stripped and refinished, which is why a rejected brushed batch is expensive.

Why does the grain look different at the edges?

The brush head slows or lifts at the end of a pass, and edges see less pressure. A shop that brushes past the edge of the part on a fixture avoids it. If your panel has a chamfer, decide whether the chamfer is brushed with the face or left as machined, and say so.

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Keep reading

This guide is part of Finishing Audio Parts: Anodize, Brush and Blast, one of four sections in the guide library.