Finishing geometric intarsia

Why finishing geometric intarsia is different

On a single-coloured wooden surface a finish works evenly: one species, one way of absorbing, one result in reflection. On geometric intarsia, several species with different pore structures, colour temperatures and rates of absorption meet one and the same coat of finish. The result is never just the sum of the single effects; it is an interplay that shows most clearly at the joints and transitions.

An oil that gives wenge a rich, dark depth behaves differently on the neighbouring ash: it warms the light tone, adds yellow and changes the gap in lightness between the two species. That can increase the contrast or shift it in an unwanted direction, depending on the colour temperature the finish brings.

Mistakes in finishing cannot be undone without putting the geometry at risk. More sanding to correct them costs veneer thickness, rounds geometric edges and opens joints. That is why good finishing of geometric intarsia does not start with the brush, but with a test on identical sample material in real light.

How contrast changes under a finish

Contrast in geometric intarsia is not a fixed value; it is a perceived gap in lightness that changes with every surface. In the raw, unfinished state, veneer often looks less contrasting than after the finish, because dry wood fibres scatter light evenly and weaken differences of colour.

Oils saturate wood fibres and partly fill pores. That usually deepens dark species more visibly than light ones. Wenge becomes richer and darker under oil; ash becomes slightly warmer but stays light by comparison. The contrast between the two rises.

Wax affects all species more evenly. It creates less depth in the fibres than oil and so changes the contrast less dramatically. That can be an advantage when an existing balance of contrast is to be kept. It can be a drawback when the pattern is only meant to reach its full effect under the finish.

Shellac deepens all colours, but increases the richness especially on dark species. In pairings of wenge and walnut, shellac can reduce the contrast between the two similarly warm species, because both are pulled into the same deep brown. In pairings of wenge and ash, pale shellac can widen the gap, because ash stays light while wenge looks almost black.

How reflected light changes the way geometry is seen

Geometric patterns are perceived not only through contrast but also through reflection. The way a surface reflects light influences which geometric lines are visible from which angle. On a small desk object such as a pen holder, light comes from a typical desk-lamp position: at an angle from above, from one direction. Under this light, matt and glossy surfaces behave very differently.

A matt surface scatters light diffusely and shows the pattern almost evenly, whatever the angle of view. The lines of the pattern stay visible, but look without depth. A glossy surface concentrates light at one angle of reflection and, seen from that direction, creates a strong mirror reflection. In that zone the lines of the pattern can disappear behind the reflection.

Satin surfaces sit in between and usually work best on geometric intarsia objects: they show the depth of the wood, but create no concentrated reflection that outshines the boundaries of the pattern. The actual reflection depends on the pore structure of the species, the thickness of the finish and the state of the sanding before the finish goes on.

Pore structure and geometric sharpness

Pores are openings in the wood surface whose size and distribution depend on the species and the cut. Open, coarse pores as in wenge or oak scatter light at the surface and create a micro-textured effect. Ash is coarse-pored too. Fine pores as in maple scatter less and make the surface look smoother under the same finish.

At geometric transitions between two species with different pore sizes, sharpness can suffer. A clean joint between wenge and maple looks sharpest under light when both surfaces reflect alike. If the wenge is coarse and open and the maple smooth, the two sides of the joint reflect differently, and the boundary can look less sharp.

Grain filling can reduce this difference. A grain filler, or several coats of a building finish with sanding in between, fills the open pores until both surfaces reflect alike. The result is a more even edge, even in pairings with very different pore structures. The price is a more closed look that shows less of the wood's texture.

Matt, satin and high gloss on geometric patterns

The sheen of a finish influences how geometric patterns appear from different angles and in different light. No sheen is right everywhere; each has its own effects on geometric compositions.

Matt surfaces show patterns evenly from every angle, but make the colour and depth of the wood look restrained. On very light species such as ash, too flat a matt can make the veneer look dull and visually cheapen the wood. On dark species matt can make sense when the texture of wenge or walnut is meant to come first, not the sheen.

Satin surfaces give controlled depth without concentrated reflections. They work well on small desk objects seen under a spot or desk lamp. Satin lets the wood show its figure and its colour temperature without disturbing the geometric pattern with bright spots.

High gloss is unsuitable for geometric intarsia in most cases. Strong gloss on small surfaces creates large bright spots at typical viewing angles that visually cover the lines of the pattern. In pairings of wenge with a light wood, high gloss can turn the contrast into a restless scatter of light that dissolves the geometric intent. There are exceptions for particular formats, but they call for very careful control of the surface and of the light the piece stands in.

Open-pored or filled

Open-pored surfaces show the texture of the wood directly. The pores stay visible and can be felt. That is honest craft and emphasises the character of the material. On geometric intarsia with several species, however, a problem arises: different pore sizes scatter light differently on neighbouring areas, which makes geometric edges look softer.

Grain filling is a step before or during the build-up of the finish in which the pores are closed with a filler or with built-up coats of finish. After filling and a targeted sanding the surface is level, reflections become more even and geometric transitions look sharper. That matters most where wenge meets a fine-pored species directly.

The drawback of grain filling is a loss of texture. The visible pores are part of the visual character of wenge and oak; closing them completely makes the surface more neutral. How far to fill depends on the character wanted for the finished object. For objects dominated by geometry, more filling can make sense, as long as the film does not get so thick that it bridges the joints (lacquering). For objects centred on the material, more open texture makes sense.

Darkening and stronger contrast

How much a finish darkens wood depends on the species and does not grow in step with the amount of finish. Wenge darkens strongly under oil: raw, wenge often looks greyish brown; oiled, it becomes a deep blackish brown. This effect appears with the first coat and hardly increases with further coats. Darken wenge too much and the inner texture of the fibres is lost.

Walnut darkens moderately and takes on a warm, chocolate tone under oil. The pores fill optically and the figure becomes clearer. Oak darkens less than walnut, but gains warmth and a yellow tone. Ash hardly darkens and stays light under oil, but loses its very pale, almost white look and takes on a soft cream tone.

These differences in darkening change the contrast of the finished object compared with the raw veneer. Anyone planning a pattern with a particular contrast in mind has to anticipate the state after the finish, not the raw one. Planning contrast therefore does not end with buying the veneer, but only after the finish test.

Edges and transition zones

At geometric transitions between two species, unwanted effects can appear at edges and transitions. Dark dust, above all sanding dust from wenge, can be carried into the open pores of the neighbouring light species when liquid oil is applied. The result is a dark zone at the joint that looks wider than the actual cut line.

This transfer happens mostly when oil is brushed or wiped across joints with too much pressure. Thorough dusting before application, with a brush and a vacuum cleaner or compressed air, removes the dark dust from the light pores; applying with little pressure and along the grain reduces the risk further.

Finish can also build up at edges when too much is applied. Oil that collects at a veneer edge and dries there forms a small shiny bead that shows as a line of light after finishing. This line is immediately visible at high-contrast edges between wenge and light species. Wiping off excess oil before it dries prevents it.

Differences in absorption between species

Different species take up finish to different degrees. Wenge has large, open pores that can soak up a lot of finish, while the dense fibres between them take up little. Some workshops report that finish dries more slowly on wenge; a sample shows how your own product behaves.

Ash and oak take finish up quickly and evenly. A coat that is right for one species can be too much on the next and leave too heavy a layer. Once dry, this layer shows as a zone of different sheen right at the joint, which picks out the joint line.

The practical consequence is that a single even coat over the whole composition does not produce an even effect. Thin coats and thorough wiping off of the excess largely even out the differences; a sample made of the same woods shows beforehand how well.

A consistent finish across several species

The aim when finishing geometric intarsia is consistency: the same sheen, the same depth and the same density of reflection across all the species involved. That aim is harder to reach than with a single species, because each species reacts differently.

One method is selective application: species that take up a lot get an extra thin coat before the whole surface is treated together. That calls for exact knowledge of how each species absorbs and a trial run before the actual finish.

A second method is choosing a finish that naturally creates little difference between species. Waxes and many hard-wax oils react more evenly than pure oils and give a more similar sheen on all species. The drawback is that they also give less depth than oil or shellac systems.

Durability and a clean look

Hard lacquers such as polyurethane protect best against scratches, moisture and abrasion. But they lay a film over the wood, and on small objects that are looked at closely and picked up, this film can often be seen and felt (lacquering).

Oil, hard-wax oil, wax and shellac are less resistant to abrasion, but show the character of the wood more clearly. On a pen holder that stands on a desk and is rarely put under heavy strain, maximum hardness matters less than look and feel.

The relevant question is not whether the surface needs maximum protection, but what strain the particular object will meet in typical use. A coaster needs more protection from water than a wall piece. A desk object needs more resistance to abrasion than a pure display piece. Caring for handmade wooden objects describes how finished pieces are looked after.

How Reihax finishes its surfaces

Reihax treats finishing as part of the geometric quality, not as a separate last step. The question is: which surface keeps the lines clearest without overriding the character of the wood?

The answer is the same for every current Reihax piece: hard-wax oil in a satin sheen, in two thin coats with a light sanding with a fine abrasive pad in between. Satin keeps the reflected light calm. High gloss would create bright spots on small objects under a desk lamp that cover the lines of the pattern.

Protecting the contrast means that the gap in lightness between dark and light species survives the finish. Every oil deepens the tones and warms light woods slightly. How that plays out with different pairings, for example in the variants of THINK BIGGER, is shown on the page contrast and colour temperature.