Colour, white and varnish: how UV printers print layer by layer
are explained briefly when you hover over or tap them.
A UV printer can print layers on top of each other because each layer hardens immediately. That is exactly what makes it so versatile: with white as a base coat, colours glow even on black wood, and with varnish a design gains gloss or texture. Which order you choose determines appearance, print time and ink consumption.
The three building blocks
- Colour (CMYK): is translucent, so slightly see-through. On a white substrate it looks as planned, on a dark one hardly at all.
- White: covers the substrate and serves as a base coat for the colour.
- Varnish: clear, for gloss, protection or tactile effects.
Because colour is translucent, almost every layer decision comes down to one question: what is behind the colour, and from which side is it viewed?
The most important orders
| Order | When | Result |
|---|---|---|
| colour only | white or very light substrate | thin, fast, substrate shows through slightly |
| White, then colour | dark, coloured or transparent substrate, viewed from the front | colours glow as on paper |
| Colour, then white | transparent material, viewed from behind (glass, acrylic) | print the design mirrored, white covers the back |
| Colour, white, colour | transparent material, viewed from both sides | coloured on both sides, for example window pictures, acrylic stands |
| … plus varnish on top | as the last layer in any variant | gloss, protection or texture |
White under colour
The standard for anything that is not white: dark wood, slate, anodised aluminium, coloured plastic. Without white, light shades almost disappear completely. On natural-coloured wood, however, printing without white can be intentional. The grain then shows through, which often looks more natural.
A tip: do not print the white all the way to the edge of the design, but make it minimally smaller. Otherwise a white edge flashes out if there is slight misalignment.
Reverse printing: colour, then white
With glass or acrylic that is viewed from the front but printed on the back, you print the colour first and the white over it. The design usually has to be mirrored; some printer software does this automatically with this setting. The advantage: the print sits protected behind the pane, and the front stays smooth and shiny. Roland DG, for example, describes this order for backlit acrylic pictures.
Colour, white, colour
For objects visible from both sides. The white layer in the middle separates the two colour layers. The colour layer that is later viewed through the transparent material usually has to be set up mirrored, so that text and design appear the right way round from that side. Whether you set this yourself or the software takes care of it depends on the printer. This variant costs the most time and ink.
Varnish on top
Varnish is typically applied as the last layer, although depending on the application and software there are other builds too. It can be printed over the whole area, only on individual areas (spot varnish) or in several layers for tactile effects. More in Relief and texture.
White density and passes
A single white layer does not always cover completely. On very dark material the substrate shows through slightly, and colours then look duller. There are two adjustments for this:
- White density: Many programs allow a setting in percent. More density means more ink per area.
- Several passes: White is printed two or three times on top of itself.
How much white you need depends heavily on the opacity of the ink. Roland DG points out that weakly opaque white inks need several passes, which costs more ink and time. Make a test print with stripes of different white density on your material and decide by eye.
Too much white has drawbacks: the layer becomes thicker, the edge more tangible, and it can crack more easily when bent.
Effects on time and ink consumption
Each additional layer is, in principle, another printing pass over the same area. Roughly:
- Colour only is fastest.
- White plus colour takes noticeably longer; depending on the machine, it prints both in one pass or one after the other.
- Colour, white, colour plus varnish can take many times the print time of colour alone.
For ink consumption, white is often the biggest item, because it is printed over the whole area and densely. White ink is also more expensive than colour at many manufacturers. The printer software often shows an estimate before printing. Use it to compare variants.
Setting it up in the file
Which layer is printed where, you define either in the printer software or already in the graphics file, for example via separate layers or spot colours for white and varnish. How exactly this works is explained in Preparing print data.
For business
Define a fixed layer order for each product and document it: material, white density, number of passes, varnish yes or no. This way a reprint looks exactly like the original. White and varnish drive unit costs and print time the most. For small series it is worth checking whether a design also looks good with less white.
Continue with: Preparing print data and Varnish in UV printing.