Printing on Acrylic and Glass: Front, Back and Double-Sided

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Transparent materials have a special advantage: you can print on them from behind. The design then sits protected under the sheet and looks deep and glossy through the material. For this to work, the order of the layers, mirroring and adhesion have to be right.

Front printing, reverse printing, double-sided

Front printing is like on any other material. Without white underneath, the colours stay translucent.

Reverse printing (printing behind glass) is the most popular variant for photos on acrylic and glass. The file is mirrored horizontally, because you will later view it from the other side. The colour goes onto the sheet first, then white as a cover behind it. That way, looking through the material from the front, you see the colour first. If you swap the order, you only see a white surface.

Visible from both sides works with a sandwich of colour, white and colour again. This is typical for acrylic standees that should look good from both sides. Because the two colour layers are mirror images of each other, you need two matching layers in the software. More on layer logic in Colour layers.

Glass: it does not work without primer

Glass is one of the smoothest surfaces there is. UV ink can look good at first and later peel off in shreds. That is why on glass the following always applies:

1. Clean thoroughly with isopropanol and a lint-free cloth, let it dry.
2. Apply glass primer thinly and let it flash off.
3. Print promptly.
4. After printing, allow time to cure and only then test.

On mirrors the same applies to the glass side. The mirror coating on the back is delicate and should not come into contact with solvents. More on primer types in the article on primer.

Acrylic: film, dust and static

Acrylic holds ink better than glass, but depending on the sheet not always well enough. Many manufacturers offer their own acrylic primer. First do a test without primer using adhesive tape. If the print holds, you can do without it.

Typical pitfalls with acrylic:

• Protective film: acrylic sheets often have film on both sides. Clear transparent films are easy to overlook. If you print on the film, you pull the design off with it later. Check corners and edges.
• Static charge: when you peel off the film, the sheet becomes charged and attracts dust. Every speck of dust becomes visible in the print. An ionising blower neutralises the charge without leaving a film. Peel off the film only just before printing.
• Overspray: statically charged sheets can attract fine ink mist. This looks like a grey haze next to the design. More on this in Blurry and overspray.
• Cleaning: some types of acrylic react sensitively to high-percentage alcohol and develop fine cracks. Follow the sheet supplier’s recommendation.
• No flame treatment: acrylic is combustible. Flame treatment is not an option here.

Edge sharpness and detail

On transparent material every blurred edge is noticed immediately, because the background stays clear. For sharp edges:

• distance between print head and sheet as small as the manufacturer recommends
• lay the sheet flat, fix thin sheets in place if necessary
• make the white minimally smaller than the colour (often only fractions of a millimetre), so that no white edge shows through at the front in reverse printing

The exact underfill depends on the machine and positioning accuracy. A test print shows whether an edge is visible.

Acrylic standees

Standees with a foot, keyrings and character figures made of acrylic are a typical product for small shops. Usually you print first and then cut with the laser, or the other way round, printing onto pre-cut blanks.

If you use pre-cut blanks, you need a jig so that every part sits exactly. How to solve this is explained in Positioning. If you cut after printing, allow some distance between the design and the cut edge. Right at the laser edge, the heat can discolour the ink.

Dishwasher: no

Printed glasses, glass mugs and acrylic parts do not belong in the dishwasher. Hot water, detergent and knocks loosen UV ink on glass after a few cycles, even with primer. Manufacturers only state dishwasher resistance for combinations of ink, primer and material specially approved for it. For your customers this means: hand wash, no soaking, no scouring pads.

For commercial use

Reverse printing on acrylic is one of the highest-quality products you can print with UV and withstands everyday use well, because the design sits protected behind the material. With glass, on the other hand, you should be careful about what you promise. Put care instructions on every product page and in every shipment. That saves discussions when the first dishwasher complaint arrives after a few weeks.

Continue with: Colour layers, Primer and the materials overview.