Subsurface Laser Engraving: What
Is It & How Does It Work

Subsurface laser engraving focuses a laser to a precise point beneath the surface of clear glass or crystal. Only at that focal point does the energy create a tiny white dot — the surface itself stays smooth and intact. Repeated thousands of times, these dots build a 2D image or a full 3D model that appears to float inside the block, an effect hobbyists call a "bubblegram".

For a long time this effect belonged to industrial workshops with large, expensive green-laser systems. That has changed. With a desktop UV laser and the right crystal blanks, subsurface laser engraving is now something you can do on a benchtop at home or in a small shop.

This guide explains what the process is, how it works, which materials to use, and gives you a step-by-step guide for making subsurface laser engraving projects.

How Does Subsurface Laser Engraving Work?

The whole technique depends on one idea: controlling exactly where the laser's energy is released. A subsurface laser is focused so that its beam is harmless as it travels through the surface and only reaches a damaging energy density at the focal point deep inside the material. That spot micro-cracks into a bright pin-point, and the surrounding glass stays clear.

A few factors make this possible:

• Focal depth control. The machine adjusts the focus along the Z-axis so dots can be placed at different depths, which is how a flat image becomes a layered 3D scene.
• A dot matrix, not a line. Instead of "drawing," the laser plots a 3D grid of points. Denser dots read as brighter, lighter areas of your image.
• The right wavelength. Pulsed green lasers (532 nm) are the long-standing industry standard for crystal subsurface work and create bright, high-contrast points. UV lasers (355 nm) also engrave inside glass and are extremely precise; they are what bring this capability to compact desktop machines.

Subsurface vs. Surface Engraving: Different Requirements

Surface laser engraving and subsurface laser engraving place very different demands on both machine & material.

The machine. Surface engraving only marks the outside, so a wide range of lasers can do it — the beam just has to react with the surface. Subsurface engraving is stricter: the beam must pass through the surface untouched and release its energy at a focal point deep inside, which takes a laser that can focus tightly below the surface with precise depth (Z) control. A standard surface engraver can't do this. The xTool F2 Ultra UV includes a dedicated UV inner-engraving mode built for exactly this.

The material. Surface engraving doesn't need a clear material — opaque or colored glass, metal, wood, and acrylic all work, and glass is usually frosted on the surface. Subsurface engraving needs the opposite: a highly transparent, optically clean material so the beam reaches the focal point without scattering. Bubbles, color, or cloudiness ruin the result. K9 crystal is the standard — clear, hard, and bubble-free.

How to Do Subsurface Laser Engraving: Step by Step

Here is the real workflow for engraving inside a K9 crystal blank with a UV laser like xTool F2 Ultra UV. The crystal block is the easiest place to start; crystal balls add one extra trick.

A. Engraving a crystal block

1. Prepare your design. Use a clean black-and-white image, vector logo, or a 3D model. Higher contrast gives clearer dots.
2. Clean the blank. Wipe the top processing surface with alcohol and handle the crystal with gloves — fingerprints and dust on the entry surface degrade the result.
3. Load the material settings. Select the inner-engraving glass so the focus, power, and depth are set for you.
4. Place and size your design. Position the image inside the engraving volume and scale it; for 3D models you can adjust length, width, and height.
5. Choose dotting or scanning. Dotting produces a finer, more detailed look; scanning is faster for larger fills.
6. Run the job.
7. Finish and display. Clean the surface and set the piece on a light base to make the design pop.

B. Engraving inside a crystal ball

> Detailed Guide to Subsurface Laser Engraving Glass Ball

A sphere behaves like a lens: it bends the incoming beam and shifts the focal point, which distorts the engraving (the "spherical lens effect"). The fix is to submerge the ball in inner engraving oil so the beam enters as if through a flat surface.