Mirror & Lit-Edge Acrylic Signs
Two specialty CO2 techniques that produce dramatic results: back-engraving on mirrors (the engraved area becomes "see-through") and lit-edge acrylic signs that glow from within when paired with LED light bases.
Mirror back-engraving
A mirror is a sheet of glass with a reflective coating on the back. CO2 from the back side ablates the coating where you engrave, producing a clear "engraved" pattern visible through the glass.
Workflow
- Mirror your design horizontally, you're working on the BACK side, so the design needs to be flipped to read correctly from the front.
- Mask the BACK of the mirror with painter's tape or transfer tape, protects the mirror coating from incidental smoke contamination.
- Place mirror BACK SIDE UP on the bed.
- Focus on the back coating (not the front glass).
- Engrave at the appropriate settings.
- Peel mask after, the engraved area shows through cleanly.
Settings: typical mirror back-engrave
| Speed | 300 mm/s |
| Power | 25-35% |
| Line interval | 0.06 mm |
| Air assist | Off or very low |
| Passes | 1 |
Tips
- The mirror coating layer is thin (microns); single pass suffices on most mirrors.
- Cheap dollar-store mirrors work great, coating ablates clean.
- Premium "first-surface" mirrors (used in optics) have the reflective layer on the FRONT, you can't back-engrave these. Stick to standard household mirrors.
- Avoid running multiple passes, risk of cracking the glass.
Lit-edge acrylic signs
The classic "lit sign" effect: clear cast acrylic engraved on the back, mounted vertically on an LED base. Light enters the acrylic from the bottom edge, travels through total internal reflection, and SCATTERS at the engraved areas, producing a glowing design visible against the dark/clear acrylic.
Material requirements
- Cast acrylic ONLY. Extruded gives a fogged engrave that doesn't catch light cleanly.
- Clear acrylic, 5-10mm thick. Thicker = more dramatic depth perception.
- Polished edges, laser-cut acrylic edges work fine. If edges are rough or sanded, light won't enter cleanly.
Workflow
- Design the artwork.
- Mirror horizontally, you're back-engraving.
- Place acrylic flat on the bed, BACK SIDE UP. Cast acrylic side either way; the engrave goes on the side facing the LED base.
- Focus on the engrave surface.
- Engrave at the appropriate settings.
- Mount the engraved piece into a slot on the LED base.
- Power LED, design glows.
Settings: lit-edge engrave (5mm cast acrylic)
| Speed | 400 mm/s |
| Power | 30-40% |
| Line interval | 0.06-0.08 mm |
| Image mode (for tonal) | Grayscale |
| Image mode (for outline) | Threshold or Fill |
| Air assist | Minimum, just enough to keep smoke off the lens. Higher flow rounds the engraved edges and the sign loses its edge-glow. |
| Passes | 1-2 for visible relief |
LED base options
- USB-powered LED base: common, $5-15 from Amazon/Ali. Plastic body with slot + LEDs.
- Battery LED base: for portable signs. Worse light output.
- Custom wood base + LED strip: premium look. Mount RGB strip in a wood channel; designs become color-changing.
- Color options: warm white reads "classy"; multicolor RGB reads "trendy"; specific colors (red, blue) match brand palettes.
Pricing
- Small (3×4"): $40-65
- Medium (5×7"): $80-130
- Large (8×10"): $130-220
- Premium (custom wood base + RGB): $180-350+
Common pitfalls
- Engrave doesn't glow. Air assist was too high, rounded the engraved edges so light doesn't scatter properly. Re-engrave at minimum air flow (just enough to keep the lens clean).
- Glow is dim. Engrave too shallow, increase passes or power.
- Edges are matte. Used extruded acrylic instead of cast.
- Light leaks from sides. Acrylic edges weren't laser-cut or are sanded. Re-cut to laser-polished edges.
- Engrave is over-burned. Power too high or speed too slow. Drop power 5%.