As furniture material, metal appears in parts (legs, frames, and table bases) and as a primary material for office furniture, kitchen cabinetry, utility shelving, and in some other products as well. Steel, in the form of rods, tubing, and sheets, is the most used metal. Aluminum appears in tubes and formed sections such as angles, channels, and Ts and as a material for cast legs, frames, and small parts. Alloys are used for the casting of small metal parts such as pulls and other hardware elements.
As steel is subject to rusting, it must be finished either by painting or by plating, usually with chrome plating, which can be polished or finished to a frostier (satin) surface. Stainless steel requires no finish but is hard to work and therefore expensive and suitable only for certain designs. Aluminum is much less strong than steel and is costly relative to its strength. While it does not rust, it requires a finish called anodizing to prevent its gradual corrosion, which forms a gray oxide seen on much used kitchen pots and pans. Anodizing may be done with color or aluminum can be finished with various types of paints and coatings.
Metal office furniture and utility files, cabinets, and shelving are made of steel sheet. The sheets are cut and then bent to form box shapes or, with bent flanges, shelves or tops. Parts are welded together to make up complete units. The gauge of metal used is a significant factor determining quality. Thin sheet metal can be dented easily and may cause drumming noises, a sign of flimsiness. Flat sheet metal should not "oil can" (pop in and out) and should be difficult to dent with anything less than a hammer blow. It should be impossible to put a bend or kink in any metal part through any stress of normal use. The forming of bent flanges contributes to structural sturdiness; quality sheet metal furniture often uses nested, doubled-up box forms to produce panels of great strength. Hollow cavity spaces in sheet metal furniture need to be filled with inert fiber panels to deaden drumming noises and resist denting.
In all metal furniture, the connections are crucial. Joints may be welded or mechanical, that is, held together with screws, nuts and bolts, or other fasteners. Pushing, pulling, bouncing and shaking with particular attention to joints will give a good idea of sturdiness. Metal tubes and other thin sections, even when amply strong to resist breakage, may be springly. In a chair this may be pleasant; in a desk or shelf unit excessive springiness can be annoying.
Good finishes not only attest to general quality, they also resist rust, corrosion, and damage. Look for chipped paints at edges and corners; if circumstances permit, try to chip corner or edge in some hidden location (the bottom rear of a drawer, for example). Chrome-plated finishes are harder to evaluate, since even the poorest-quality chrome looks bright and resist damage when new. However, after a short time, poor chrome plate permits rust to form, which eventually damages the plating. The best assurance of quality plating comes through the written specifications offered by reputable manufacturers.
In evaluating metal furniture, some consideration should be given to the demands the intended use will present. Folding Out door or camp furniture, intentionally lightweight and built for limited use, cannot be expected to have the toughness and durabilily that heavier construction can offer. Office furniture, built for a long life of hard use, will stand up against considerable abuse, and consequently will be heavy and correspondingly expensive.