Almost every conversation about printing on dark, clear or reflective products ends in the same place: does this job need white? The answer decides the file, the pass count, the cost and the appearance, and getting it wrong is expensive because white is not a colour that can be switched off after the artwork has been prepared.

This guide sets out the three white strategies, how the substrate decides between them, what reverse printing changes about the layer order, how white interacts with varnish, what it adds to production, and how to approve it before a run rather than after.

Why is white ink treated as a layer rather than a colour?

Because white is printed as a field, not an image.

White is normally laid down as a solid or selective underbase in addition to the colour channels, so it adds ink, passes and registration to the same square metre.

The distinction is practical rather than technical. A colour layer follows the artwork: it appears where the design has colour and disappears where it does not. A white layer frequently covers the whole printed area regardless of the design, because its purpose is to make the surface behave like a white one. That is why a panel with 30 percent colour coverage can still consume a full sheet of white ink.

It is also why white belongs in the specification conversation rather than the artwork conversation. Channel configuration is a machine decision, made at purchase, and the published configurations across this range differ: the AJ2130G/R is specified with an extended eight-colour system including white and varnish, the AJ3220EX with an extended seven-colour system, the AJ2513G/R with CMYK plus white and optional light inks and varnish, the AJ3220G/R with CMYK plus white and varnish expandable to eight colours, and the cylinder platform with four white channels for dark objects.

What are the three white strategies?

No white, selective white, or a full underbase.

Colour without white gives transparent or stained-glass effects, selective white controls opacity in chosen areas, and a full white layer separates the graphic from the surface beneath it.

The three strategies produce genuinely different products from the same artwork. Without white, the material participates in the design: light passes through a clear panel, the wood grain reads through the colour, and a coloured board shifts the whole image. With selective white, the designer chooses where that participation stops, which is how highlight effects, partial transparency and layered imagery are produced. With a full white base, the printed result is predictable on any surface, at the cost of losing the material's own character.

The choice is usually made per product line rather than per material. A shop printing coloured acrylic signage may use a full base for one customer's brand graphics and selective white for another's decorative panels, on the same machine, in the same week. The published guidance for acrylic work describes the strategies in exactly those terms, and it treats the viewing direction and the intended appearance as the inputs that determine which one applies.

How does the substrate decide which strategy to use?

By what the surface does to the colour above it.

A light board or white canvas may take colour directly, while dark, transparent, reflective and patterned surfaces usually need a white layer first.

Four substrate behaviours matter. Absorption affects how much ink the surface takes and how evenly, which is why raw MDF and plywood are described as needing dust and absorption control before anything else. Base colour shifts the printed colour: the published guidance for wood panel work notes that white can create an opaque underbase where the natural board colour would alter the artwork. Transparency changes the viewing logic, because a clear substrate is read through rather than on. And reflectivity changes apparent density, which is why the guidance for coated metal notes that white can separate colour from the metal appearance.

Patterned surfaces add a fifth case, because the substrate's own design may participate in the printed image. The published approach for ceramic tiles is to approve white opacity and colour appearance on the actual tile and artwork, since a factory pattern interacting with a printed graphic cannot be judged from a proof on a neutral sheet.

How does reverse printing change the layer order?

The file is mirrored and colour prints before white.

On clear acrylic or glass viewed through the sheet, the layer sequence reverses so the graphic is read through the material, which also protects the print from handling.

Reverse printing is used where the material should protect the decoration: the print sits behind the sheet, so scratches and cleaning affect the acrylic rather than the ink. Two changes follow from that. The artwork has to be mirrored, because it will be viewed from the opposite side. And the layer order reverses, with colour printed first and white applied behind it as a backing.

The published guidance for acrylic work describes this as a workflow decision rather than a printer setting, and lists it among the layer strategies to compare on the real material. The same logic applies to glass and to any clear panel where the customer wants the graphic protected. Where a job mixes front-viewed and reverse-viewed parts, the two are different files rather than two settings, and they should be tracked separately in production.

What does selective white do for a design?

It keeps part of the material visible in the design.

Selective white lets the grain of wood, the tone of dark leather or the finish of coated metal remain visible where the design calls for it.

Selective white is where the technique earns its margin, because it produces an effect that a transferred film cannot easily reproduce: an image that appears to sit inside the material rather than on top of it. It is also the most demanding of the three strategies, because it introduces registration between the white layer and the colour layer, and any misregistration shows as a visible outline around the exposed area.

Two design consequences follow. Fine detail and selective white interact badly, because the registration tolerance is a physical limit rather than a software setting. And the exposed material becomes part of the colour decision, which is why the published guidance for leather work notes that a white underbase can improve opacity while selective white preserves the areas where the leather colour should remain visible, and recommends comparing both on the real material.

How do white and varnish interact?

Both are layers, and both change the pass count.

Varnish can be applied overall for gloss or selectively for spot effects, and on the cylinder platform the published capability includes raised effects up to 0.15 mm.

Varnish is often specified in the same conversation as white because both are appearance layers rather than image layers, and both consume passes and registration tolerance. The published configurations reflect that: white and varnish appear together in the extended colour sets on the AJ2130G/R, the AJ3220EX and the AJ3220G/R, and as options on the AJ2513G/R.

The order of the layers matters to the finished effect. White beneath colour makes the colour readable; varnish above colour changes the surface finish; and raised effects built from multiple layers sit on top of both. Where a design uses all three, the approval sample is the only reliable way to judge the result, because the interaction between a white base, a coloured image and a raised varnish layer is not predictable from separate proofs.

What does white add to production time and cost?

Ink, passes and registration on every printed square metre.

Andresjet publishes an ink cost of approximately $0.80 to $1.20 per square metre for a full-colour print, with the figure varying by saturation and resolution.

White moves a job within that range rather than outside it, but it moves it in a predictable direction. A full underbase adds a layer whose area follows the print area rather than the artwork, and it usually requires its own pass. Selective white adds less ink but more registration risk. The published guidance for wood panel work states the trade-off plainly: white layers add ink and production time, so opacity, colour, registration and the desired wood appearance should be approved with representative artwork.

Two operational consequences are worth planning for. Drying and curing behaviour is unchanged, because UV ink cures immediately under the lamp, but stacking and handling still need interleaving on heavy panels. And waste ink rises with the number of purges, so a shop running white-heavy work should expect the waste collector to fill faster than on a colour-only mix. Ink delivery design matters here: dual negative pressure for both colour and white is published on the AJ3220G/R as a way to reduce ink purge, which is a direct cost on white-heavy production.

How should white be approved before a run?

On the production substrate, under the viewing light.

Opacity, colour, registration, texture and surface feel should be compared together, because white changes the appearance and the hand of the finished part.

The published guidance converges on the same list across materials. Approve on the actual production item, not a substitute. Compare the strategies side by side rather than one at a time, because the differences are relative. Record the construction with the approved sample so a repeat order can be matched to it. And view the sample under the lighting the customer will use, since a white base that looks correct in the workshop can read differently in a shopfront or a bathroom.

Durability sits alongside appearance. Adhesion is assessed with the tape method under ASTM D3359 and wear under ASTM D4060, both on the finished piece, because a white base that has been applied at slightly different density can behave differently under handling (ASTM D3359, ASTM D4060). Colour repeatability across repeat orders depends on the profiles maintained for that substrate and layer construction (International Color Consortium), and process control practice for industrial print environments is covered by certification and research bodies in the field (Fogra). The wider trade guidance on print process selection helps when the comparison includes a non-digital route (PRINTING United Alliance).

What the decision comes down to

White is a layer, and the strategy is decided before the artwork is finalised. Choose between no white, selective white and a full underbase by asking what the substrate does to the colour above it, and decide the layer order by asking which side of the material the customer will look at.

Then approve both appearance and durability on the production item, and record the construction with the sample so the next run can be matched to it. Substrate-specific guidance for white and varnish appears across the material collections for acrylic and wood and MDF, with the cylinder route described in the bottle and tumbler collection.