Short answer: Reverse engraving means laser engraving a mirrored design into the back face of clear acrylic so it reads correctly through the smooth front. The engraving is protected from fingers and wear, and the sheet's thickness gives it depth. Clear cast acrylic works best because it engraves frosty white; the engraving can be left frosted, back-filled with acrylic-compatible paint, or lit from the edge so it glows.
Key facts
- Artwork: mirrored (flipped horizontally) and engraved on the back face.
- Best sheet: clear cast acrylic. Trotec's processing guide says cell cast and continuous cast engrave frosted, while extruded engraves translucent with little contrast.
- Typical thickness: 1/4 to 3/8 in. for awards and signs.
- Color: back-filled with paint ("back painting" or "color filling"), usually acrylic paint.
- Crazing risk: Perspex strongly recommends annealing engraved areas before filling them with paint, especially for outdoor pieces.
What does reverse engraving look like?
From the front you see a smooth, glassy surface with the design behind it, set back by the thickness of the acrylic. Light catches the polished edges and the frosted engraving inside. Touch the front and there's nothing there: the engraving is on the back.
| Front engraving | Reverse engraving | |
|---|---|---|
| Artwork | Normal | Mirrored |
| Feel of the front | Textured where engraved | Smooth |
| Wear and dirt | Engraving can collect dust and fingerprints | Protected |
| Depth effect | On the surface | Floats behind the face |
| Paint fill | Exposed | Sealed behind the acrylic |
| Works on | Any acrylic | Clear (or lightly tinted) acrylic |
Why does the artwork have to be mirrored?
You'll view the design through the sheet, so it has to be engraved backwards on the back face, like lettering on the inside of a shop window. The sheet goes on the laser upside down and the job is flipped horizontally; laser software has a mirror or flip setting for exactly this. The front masking stays on during engraving to protect the viewing face from scratches and smoke.
If you send us artwork for reverse engraving, send it reading normally and say it's for reverse engraving; we'll mirror it. If you've already mirrored it, say so, so it isn't flipped twice. Text is the easiest thing to get wrong, so check it.
Which acrylic works best for reverse engraving?
- Clear cast acrylic is the standard. It engraves to a bright, even, frosty white, which gives the most contrast through the front. Epilog and Trotec both recommend cast for engraving.
- Clear extruded acrylic engraves clear rather than frosted, so the design looks faint. Trotec suggests engraving extruded at a 60 to 70% grayscale halftone to get some contrast, but cast is the better fix.
- Thickness: 1/4 to 3/8 in. is typical for awards and signs; it gives a good sense of depth and stands up on its own in a base. 3/16 in. works for lighter pieces, and 1/2 in. for heavy, premium awards.
- Tinted clear (gray or bronze) can be reverse engraved, but the design reads darker and less vivid.
How do you paint a reverse engraving?
Because the paint sits behind the acrylic, it's seen through a glossy clear face and never gets scratched. There are two common methods:
- Engrave, then fill. Engrave the mirrored design on the back, then fill the engraved areas with color. For the classic plaque look, paint a background color over the whole back afterward, so the design shows in color against a solid field.
- Paint, then engrave through. Universal Laser Systems' color-fill guide describes painting the back first, engraving paint-side up through the paint with the art mirrored (and sometimes inverted, depending on the background color), then filling the engraved areas with a second color. Masking lets you place several colors.
Metallic paints give a gold or silver look seen through the clear face. A dark backing or black paint over the whole back makes a frosted white engraving pop.
Caution: engraved areas carry heat stress, and many solvent-based spray paints and lacquers can craze acrylic there. Perspex says to use paints known to be compatible with acrylic and to anneal engraved sections before paint filling, especially for outdoor use. Water-based acrylic paints are the safer choice; test on a scrap first. More in how to paint acrylic sheet.
Does reverse engraving work with edge lighting?
Yes, it's the most common pairing. Light shone into the edge of a clear panel stays trapped inside by total internal reflection until it hits the frosted engraving, which scatters it out toward the viewer. The design glows while the rest of the panel stays nearly clear, and reverse engraving keeps the front smooth and free of dust that would also glow. For edge-lit pieces, leave the engraving unpainted or use translucent color. See how edge-lit acrylic signs work.
Where is reverse engraving used?
- Awards and plaques (acrylic awards and plaques)
- Office and lobby signs mounted with standoffs, where the engraving faces the wall
- Edge-lit LED signs and night lights
- Wedding and event signs
- Photo and memorial pieces, where a photo engraving is protected behind the face
Ordering reverse engraving
Upload your design and mark it as reverse engraving in the order notes, along with any paint colors. See our engraving service for what's possible and what laser engraving on acrylic looks like, then upload your artwork for a price.
Questions
Can photos be reverse engraved?
Yes. Photos are engraved as a pattern of fine dots, and reverse engraving them on clear cast acrylic gives a soft, frosted image that looks good with a dark backing or edge lighting.
Can you reverse engrave colored acrylic?
Only clear or lightly tinted acrylic, since you need to see through it. On opaque colors, engrave the front instead.
What about mirror acrylic?
Engraving the back of mirror acrylic removes the protective paint and the mirror layer, so from the front the design shows as clear or frosted shapes in the mirror, which can then be painted or backlit. Results vary with the product's backing, so test a sample.
Do I need to mirror my file before sending it?
No. Send it reading normally and note that it's for reverse engraving, and we'll flip it. If you do mirror it yourself, tell us so it isn't flipped twice.
Which side should be engraved on a wall sign?
The side facing the wall. Viewers see the design through the smooth front, and the engraving stays clean and protected.
Sources
- Trotec: Working with acrylic, laser processing guide
- Epilog Laser: Laser cutting and engraving acrylic
- Rowmark: Reverse engraving and paint filling explanation
- Universal Laser Systems: Laser processing guide, color fill
- Perspex: Design Guide, Part 1 Fabrication (laser engraving, paint filling, annealing)