Short answer: Laser engraving cast acrylic gives a bright, frosty white mark with strong contrast. Extruded acrylic engraves clear and translucent, with little contrast, so choose cast for anything that should stand out. Raster engraving fills areas with closely spaced lines, typically at 300 to 600 DPI. Line (vector) engraving scores a thin groove along a path. Decorative engraving is shallow, a few thousandths of an inch; anything over about 0.010 in. counts as deep. Engraving can be color filled, or done on the back of clear sheet so it's protected.
Key facts
- Cast acrylic (cell cast or continuous cast) engraves frosted white. Extruded engraves translucent, with little to no contrast (Trotec, Epilog).
- Raster resolution: 300 to 600 DPI with a standard 2 in. lens. Above 600 DPI calls for a 1.5 in. lens with a 0.003 to 0.0065 in. spot (Epilog).
- Depth: decorative frosting is a few thousandths of an inch. Plaskolite treats raster engraving over 0.010 in. as deep.
- Too much power in one pass leaves a white, snow-like residue in deep engraving. Several lighter passes give a crisper result (Trotec).
- Paint fill: use paints made for acrylic. Perspex recommends annealing engraved areas before paint filling, especially for outdoor use, to prevent crazing.
- Smallest readable text: about 6 to 8 pt.
What does engraved acrylic look like?
A CO2 laser engraves acrylic by vaporizing a thin layer of the surface. What's left behind depends mostly on how the sheet was made:
| Material | Engraved look | Best for |
|---|---|---|
| Clear cast | Bright, even, frosty white | Awards, signs, edge-lit pieces, photos |
| Clear extruded | Clear and translucent, little contrast | Subtle marks and low-cost parts where contrast matters less |
| Opaque colors | Lighter, matte version of the color | Labels, panels, tags; contrast varies by color |
| Mirror | Frosted marks in the acrylic face, or clear windows if the backing is engraved off | Decor and gifts |
Cast acrylic frosts because it vaporizes cleanly and leaves a fine, rough texture that scatters light. Extruded acrylic melts more easily, so the engraved surface partly re-flows and looks clearer. Trotec's guide says engraving extruded gives little to no contrast, and Epilog calls cast the better choice for engraving. If the engraving should stand out, choose cast. More in cast vs extruded acrylic.
A clear mark on cast acrylic usually points to a problem. Trotec's troubleshooting lists the beam being out of focus or too little power as the usual causes.
Raster vs line (vector) engraving
Raster engraving (fill)
The laser sweeps back and forth across the design like a printer, firing only where the artwork is filled. That's how solid areas, text, logos, and photos are engraved. Large fills take longer because the laser has to cover every line of the area.
Line engraving (vector, score)
The laser follows the outline of a shape at low power, scoring a thin groove without cutting through. It's fast and gives a crisp, delicate line, good for outlines, thin text, and line art. It's much quicker than filling the same design.
Many designs mix the two, such as filled text with a line-engraved border. In your file, keep each type on its own color or layer (how to prepare a laser file).
How deep is laser engraving in acrylic?
For appearance, engraving is shallow, usually a few thousandths of an inch. That's enough to frost the surface and catch paint. Plaskolite's fabrication guide treats raster engraving deeper than 0.010 in. as deep engraving. At that depth it suggests keeping the top masking on, because vaporized acrylic can settle back and haze the surrounding surface.
Deeper engraving is used for tactile marks, deeper paint fills, or a carved look. Trotec warns that going deep with high power and low speed leaves a white, snow-like residue in the bottom. Several passes give a crisper result. Trotec also describes a final pass with the focus moved about 1/2 in. away from normal. This melts the bottom of a deep cast engraving to a clear, glazed, molded look instead of a white one. Depth has little effect on how white a shallow cast engraving looks once it's frosted.
Speed, power, and DPI: what are the trade-offs?
Every laser is different, so exact settings don't transfer from one machine to another. Laser makers publish starting points and tell you to test. The principles do transfer:
- Power and speed together set how much energy reaches the surface. More power or slower speed means deeper engraving. Engraving usually runs at high speed and low power. Too much energy causes melting, a raised lip at the edges, and a glossy rather than frosty look.
- DPI (lines per inch) controls how close together the raster lines are. Epilog recommends 300 to 600 DPI with a standard 2 in. lens, and a 1.5 in. lens above 600 DPI. Higher DPI gives a smoother fill and finer detail but takes longer, and too high can overheat the surface. Too low shows visible lines.
- Photos are converted to a dot pattern (dithering). They usually engrave best at moderate DPI and lighter power, so the dots stay separate.
- Extruded contrast trick: Trotec suggests converting artwork to about 60 to 70% gray. The laser then engraves a halftone, which gives extruded sheet some contrast.
- Focus matters for crisp edges, especially on fine text.
We pick settings for your material and design. You don't need to supply them.
Should the film be on or off when engraving?
Makers disagree, because it depends on the job. Trotec says to remove paper or film backing before engraving: engraving through it takes more power, loses fine detail, and plastic film can melt onto the acrylic. Epilog also says to remove the top masking for engraving. Plaskolite makes an exception for deep raster engraving, where leaving the top masking on prevents haze. When an engraving will be paint filled, the masking can double as a paint mask. We choose per job.
Color filling engraving
Engraved areas can be filled with paint for color: black or a color on clear, white on dark, or metallic. The paint goes into the engraving, and masking left over the surrounding surface is peeled off to take the excess with it. Paint compatibility matters, because some solvent-based paints craze acrylic. Perspex recommends annealing engraved areas before paint filling, especially for outdoor parts, to prevent crazing later. See how to paint acrylic sheet.
Front vs reverse engraving
- Front engraving works on any acrylic. The design is on the surface you look at and is slightly textured to the touch.
- Reverse engraving works on clear acrylic. A mirrored design goes on the back and reads through the front, protected and with a sense of depth. Epilog notes that the artwork has to be mirrored before engraving. See reverse engraving acrylic.
For edge-lit signs, either works, and reverse keeps the front smooth (how edge-lit signs work).
How small can engraved text be?
Engraved text stays readable down to about 6 to 8 pt (capitals about 1/16 in. tall). Thin fonts below that get fuzzy, and bold, simple fonts hold up best. For tiny details, engraving beats cutting (smallest laser-cut detail).
Ordering engraving
Put engraving on its own color or layer in your file and note it in your order. We treat lines as cuts unless told otherwise. See our engraving service for filled, line, front, and reverse engraving, then upload your artwork.
Questions
Do you engrave acrylic with the film on or off?
Usually off for crisp, fine detail. Trotec and Epilog both recommend removing the top film, which can melt or blur the engraving. The film is left on for deep raster engraving or when it serves as a paint mask.
Can you engrave black acrylic?
Yes. Engraved black acrylic shows a gray, matte mark. For bright white contrast, it can be color filled.
Why is my acrylic engraving clear instead of white?
Most often the sheet is extruded, which engraves translucent. On cast acrylic, a clear mark usually means the beam is out of focus or the power is too low, according to Trotec's troubleshooting guide.
Does laser engraving on acrylic wear off?
No. The engraving is part of the surface, not a coating. Paint fills on the front can wear with heavy handling. Reverse engraving protects them.
Why does engraved acrylic smell, and for how long?
Freshly lasered acrylic gives off leftover monomer vapor. Trotec suggests keeping parts in a well-ventilated area for about 48 hours, which cuts the odor a lot.
Sources
- Trotec: Working with acrylic, Laser Processing Guide
- Epilog Laser: Acrylic laser cutting and engraving
- Epilog Laser Support: Focus Lens 101 (lens choice and DPI)
- Plaskolite: OPTIX-L Continuous Cast Acrylic Sheet Fabrication Guide (laser engraving)
- Perspex: Design Guide, laser engraving and paint filling