Finishing

Also called: french polishing, polishing, oiling, waxing, staining, lacquering

Finishing is the last stage of working a piece of wood: the treatment given to its surface once shaping is complete, ranging from a final smoothing pass with a plane to staining, sealing or polishing before the piece is done.

Preparing the surface

A finishing plane takes the very last pass over a surface, removing the ridges left by earlier planing strokes. On tropical woods with interlocking grain, where the fibres spiral in alternating directions up the trunk, planing across the grain with a very fine-set blade is sometimes advisable, since it can cut such wood more cleanly than the ordinary along-the-grain pass; a final pass along the grain, made with a scraper plane freshly sharpened for the job, then follows to true the surface up. For the finest surface work, and for the polishing stage itself, 240-grit abrasive is used. Whatever method or material is finally chosen, the quality of a finish depends on the surface preparation that lies beneath it.

Matching the finish to the timber

Timber species react differently to finishing materials. Oak, sweet chestnut, camphorwood, Douglas fir and afromosia are prone to strong staining reactions, while African mahogany, idigbo, sapele and several related timbers react only slightly, causing minor staining by comparison. A finish product's own label states which stains and sealers suit it, and it usually warns against materials that would clash with it, so checking the label against the timber in hand is worth doing before starting.

French polishing

French polishing, building a shine with thin coats of shellac, begins once the open grain, the small surface pores left visible after preparation, no longer shows. It uses bleached shellac, shellac that has been lightened in colour. One described method uses slightly more oil in the polish than most French polishers use, in the words of Jones (1920), 'a trifle more oil than most french polishers generally use.'

Finishing on site or in the factory

Interior wood finishing takes many forms, given the range of wood products and applications it covers, from floors to cutting boards. Where finishing happens also matters: doing it at the factory rather than on site gives a more consistent film thickness, avoids the light exposure and bad-weather problems on-site work can run into, and can speed up completion of a structure while lowering its overall cost.

Finishing the joint, not just the surface

Finishing is not only a matter of surface treatment. Traditional Japanese carpenters shaped joint faces in varied ways, such as the hako-dome and daiwa-dome joint forms, specifically to stop mitres and other joints from opening up over time, treating the fit of the joint itself as part of getting the finish right.