Surface texture, no coating

Mechanical finishes

Brushing, polishing and blasting change the surface texture without adding a coating.

These processes remove or displace metal rather than adding a layer, so nothing changes the part dimensions in any way you have to allowance for. They are usually the first step in a finishing sequence — brushed or polished aluminium is then anodised to lock the appearance in.

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How it compares

Relative to the other finishes we apply. A selection aid, not a specification.

Corrosion resistance Limited
Wear resistance Fair
Colour range Limited
Edge and recess coverage Fair
UV stability Excellent
Repairability Good

How the process works

Belt grinding to remove extrusion die lines and deep marks.
Brushing with abrasive-impregnated wheels to lay a directional grain.
Polishing with progressively finer compounds to a mirror finish.
Sandblasting or glass beading to produce a uniform matte texture.
Tumbling or vibratory finishing for small parts and deburring.

Thickness and systems

Option	Range	Note
Brushed	No film	Directional satin grain. Usually anodised afterwards to seal it.
Polished	No film	Mirror or satin polish. Very susceptible to fingerprints and oxidation if left bare.
Sandblasted / beaded	No film	Uniform matte. Hides die lines and small surface defects well.

Typical properties

Property	Value
Material removed, brushing	5–20 µm
Material removed, polishing	10–50 µm
Achievable roughness, brushed	Ra 0.4–1.6 µm
Achievable roughness, blasted	Ra 1.5–3.5 µm
Achievable roughness, polished	Ra 0.05–0.2 µm

Advantages

Keeps the natural metal appearance rather than covering it.
No dimensional allowance needed for a coating thickness.
Blasting hides extrusion die lines and is the cheapest way to a uniform look.
Polishing gives a genuine mirror finish that no coating reproduces.
Localised repair and re-brushing is practical, unlike anodising.

Limitations

Bare mechanical finishes offer almost no corrosion protection — aluminium oxidises and marks.
Polished surfaces show every fingerprint and water mark.
Brushed grain direction is visible and has to be specified consistently across a part.
Sharp edges under-blast and can look different from the flat faces.
Hand finishing means batch-to-batch variation; supply a master sample.

Design notes

What costs money when it is discovered after tooling.

Almost always follow with clear anodising — bare brushed or polished aluminium will not stay looking new.
Specify grain direction on the drawing; on a long profile it is very visible.
Blasting is the most forgiving option over a complex section with many edges.
High polish plus anodising slightly reduces the gloss; allow for it when matching a sample.
Fingerprints are the main complaint on polished parts — consider a clear e-coat or lacquer.

Colour and effect range

Natural aluminium only
Colour comes from a subsequent anodising step

Standards

No single standard — specify Ra and grain direction on the drawing
Often quoted with a following ISO 7599 anodising step

Typical applications

Consumer electronics and audio equipment
Architectural trim and handrails
Decorative panels and signage
Automotive interior trim
Kitchen and appliance surfaces

Other finishes

Conversion coating

Anodising

An aluminium oxide layer grown out of the metal itself — hard, integral and never peels.

Electrodeposited organic coating

Electrophoretic coating

Paint deposited by electric current, so every edge and recess gets the same film.

Applied organic coating

Powder coating

The widest colour and texture range of any finish we apply, with a tough cured film.

Sublimation transfer over powder

Wood grain transfer

A photographic wood or stone texture sublimated into a powder coat — the look of timber…

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