8K — also called No.8 or super mirror — is the highest reflectivity finish produced on stainless steel. Done correctly the surface reads as a true mirror: no visible grain, no haze, no distortion of the reflected image. It is also by a wide margin the most process-sensitive finish in the catalogue.
The five stages, and why none can be skipped
- Grinding. Removes mill defects, weld tone and deep scratches. If the surface is not flat and defect-free here, no amount of later polishing will make it a mirror — polishing amplifies flatness errors rather than removing them.
- Intermediate polishing. A sequence of progressively finer abrasive stages that removes the grinding pattern. The number of stages depends on the incoming condition; skipping stages is the single most common cause of a hazy result.
- Buffing. A soft wheel with a fine compound does the final work. This is what converts a fine satin into a mirror.
- Cleaning and drying. Buffing compound residue left on the surface will bloom into visible staining within days.
- Protective film. An 8K surface is damaged by almost any contact. Film is applied before the sheet leaves the line.
Every attempt to compress this sequence produces the same family of defects: orange peel, haze, or a "ghost" of the underlying grain that only appears once panels are hung.
What actually determines the result
- Base material quality. Inclusion banding and coarse grain in the steel will not polish out. This is the most common cause of a line "not being able to reach 8K" when the machine is fine.
- Flatness. Any waviness shows as distortion in the reflection.
- Coolant and compound management. Overheating during polishing draws colour into the surface.
- Cleanliness. A single particle carried into the buffing stage scores the sheet.
Where 8K is used
- Architectural feature walls and column cladding
- Decorative lift interiors and ceilings
- Retail and hospitality joinery
- Sculptural and signage work
Coil or sheet?
Both are possible, and the choice is economic rather than technical. Coil-to-coil gives throughput and consistent handling for long runs. Sheet-to-sheet gives better control when you are working with heavy plate, mixed sizes, or short runs of expensive material. Most 8K producers run sheet, because the value per sheet justifies the handling time.
Protecting the result
An 8K panel should never leave the factory unfilmed, and the film should stay on until installation. Once installed, clean only with a soft cloth and a non-abrasive cleaner — any abrasive pad, however fine, reintroduces a grain that cannot be removed on site.