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Making Brass and Copper Audio Parts That Do Not Turn Brown

August 16, 2026

Brass and copper do something aluminum cannot: they give a part real weight and a warm colour that reads as expensive the moment someone picks it up. They also oxidize continuously from the second they leave the machine, which makes them the most demanding materials in a hi-fi parts list.

Alloy choice

Alloy	Name	Machinability	Colour	Use
C360	Free cutting brass	Excellent, the benchmark	Bright yellow gold	Knobs, feet, trim, threaded parts
C260	Cartridge brass	Fair, gummy	Slightly redder yellow	Formed and drawn parts
C464	Naval brass	Good	Yellow, slightly darker	Corrosion resistance
C932	Bearing bronze	Good	Brown gold	Bearings, bushings
C110	ETP copper	Poor, very gummy	Salmon pink to red	Trim, plates, conductors
C145	Tellurium copper	Good	Copper	Copper parts that must be machined well

For machined audio parts the answer is usually C360 brass. It cuts faster and cleaner than aluminum, holds threads well and polishes to a mirror with modest effort. If your design needs actual copper appearance, C145 tellurium copper is far easier to machine than C110 and looks close enough.

Note that C360 contains lead. If the part is sold into a market or a product category with lead restrictions, check before specifying it. Lead free alternatives such as C69300 or C87850 exist, machine slightly worse and cost more.

Finishing routes

Polished and lacquered

The classic bright brass look. Polished mechanically or by tumbling, degreased thoroughly, then clear lacquered.

• Lacquer types: acrylic air dry, two part polyurethane, or a UV cured clear. Two part is the most durable.
• The critical step is cleaning. Any fingerprint or polishing compound left under the lacquer shows as a permanent cloudy patch.
• Specify the lacquer type and an adhesion test if the part gets handled, which a knob obviously does.

Brushed or bead blasted, then lacquered

A satin brass that shows fingerprints less than a mirror finish and hides handling marks. Increasingly the preferred look on modern high end audio.

Patinated

Chemical darkening to brown, near black or a green verdigris, then sealed with wax or lacquer. Beautiful and almost impossible to repeat exactly across batches. Treat it as a hand finish, approve every batch against a sample and tell the customer the variation is intentional.

Electroplated

Nickel, black nickel, chrome, gold or rhodium over the brass.

• Hard, stable, no tarnish, and a completely different appearance from the base metal.
• The plating reproduces the surface underneath, so a part must be polished or blasted before plating exactly as if the plating were not there.
• Black nickel on brass is a common and very handsome combination on knobs and feet.

Left bare on purpose

Some designs want the part to patinate with the owner. That is a legitimate choice. Say it explicitly on the drawing and in the customer documentation, and ship the parts with a corrosion inhibitor so they arrive bright and start their life from there.

The handling problem

Bare brass and copper record every fingerprint, and the salt in a fingerprint etches. On a part that is polished and waiting for lacquer, a bare hand for two seconds causes a permanent mark.

What to require from the shop:

• Gloves from the polishing operation onwards, without exception
• Minimum time between final polish and lacquer or plating
• Degrease immediately before coating, not the day before
• Parts individually wrapped after coating, never bulk packed
• Corrosion inhibitor paper or VCI bags for any bare part in transit

Write these into the PO. They are not standard practice at every shop and they are the difference between a good batch and a brown one.

Cost realities

Brass is roughly three to four times the price of aluminum per kilogram, and it is roughly three times as dense. For the same part geometry, the material cost can be ten times higher. That is the main line on the quote, not the machining, because brass cuts faster than aluminum.

Copper is worse: expensive, dense and slow to machine because it is so gummy. A copper part is a statement piece, priced accordingly.

Practical consequences:

• Hollow out the underside of a brass knob if weight allows. You keep the feel, you lose the material cost.
• Consider a brass skin over an aluminum core for large parts, though the joint becomes a visible line.
• Ask for the offcut to come back, or for the material to be credited. Brass swarf has real scrap value and on a large order it is worth negotiating.

Drawing notes that work

MATERIAL: BRASS C360 PER ASTM B16
FINISH: POLISH TO MIRROR, DEGREASE, TWO PART CLEAR LACQUER
NO BARE HAND CONTACT AFTER POLISHING
PACK INDIVIDUALLY IN VCI PAPER, DO NOT BULK PACK
APPEARANCE TO MATCH APPROVED SAMPLE

For plated parts, add the plating specification and the underlayer:

FINISH: BEAD BLAST #120, ELECTROLESS NICKEL 8-12 MICRONS,
THEN BLACK NICKEL, SEALED

Frequently asked questions

Keep reading

• Which Aluminum Alloy to Use for an Anodized Audio Part
• Anodize Colour Matching Across a Batch and Across a Year
• How to Specify a Brushed Finish on an Audio Front Panel

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