Material Identification
Customer brings you "stainless steel" or "an acrylic sign", but is it actually safe to laser? How do you tell? Material identification prevents disasters and ruined parts. Here's the working knowledge.
Stainless steel: alloy variants
"Stainless" is a chemistry range, not a single material. Different stainless alloys color differently under fiber laser annealing.
| Alloy | Composition | Identification |
|---|---|---|
| 304 (most common) | ~18% Cr, ~8% Ni | Magnetic? No (austenitic). Sparkle test: short orange sparks. |
| 316 (marine grade) | ~17% Cr, ~10% Ni, ~2% Mo | Non-magnetic. Costs ~30% more than 304. Tag often says "316L" or "marine." |
| 430 (cheap) | ~17% Cr, no nickel | MAGNETIC (ferritic). Common in budget cookware. |
| 17-4 PH (hardened) | ~15-18% Cr, 4% Ni, Cu | Magnetic. Used in firearms, aerospace. |
Quick test: magnet. 304 and 316 don't stick; 430 sticks. Color anneal results vary. Always test new lots.
Aluminum: anodized vs raw
- Anodized: looks like a colored aluminum surface (black, red, blue, etc.). Has a glassy clear oxide layer dyed with color. Tap on it, sounds like metal. Scratch lightly with a fingernail, leaves no mark.
- Raw aluminum: dull silver, sometimes brushed. Easily scratches. Reflects light like polished metal.
- Cast vs extruded vs sheet: extruded has visible grain along extrusion direction; cast has rougher texture.
Quick test: colored = anodized; bare silver = raw. Both are aluminum but lase very differently.
Acrylic: cast vs extruded
The two acrylics laser DIFFERENTLY. Cast = great. Extruded = bad on CO2.
| Type | Identification | CO2 result |
|---|---|---|
| Cast acrylic | Uniform color throughout. Sharp clean edges from manufacturer. Slightly more expensive. | Flame-polished (clear) edges |
| Extruded acrylic | Slightly cheaper. Sometimes has a faint stripe or banding when held to light. Often labeled "extruded" or "sign-grade." | Matte/foggy edges (looks DIY) |
Quick test: ask the supplier. Reputable suppliers (TAP Plastics, Inventables) clearly label cast vs extruded. If buying generic, assume extruded, Amazon "acrylic sheet" is usually extruded.
Plastics: what's safe to laser
| Plastic | Safe? | Identification |
|---|---|---|
| ABS | OK | Foamy lightweight. Slightly toxic when burned but manageable with extraction. |
| PEEK | Excellent | Honey/amber colored. Premium engineering plastic. |
| Acrylic (cast) | Excellent | See above. |
| Polycarbonate (Lexan) | BAD | Smells sweet when burned. Yellow burn, not clean cut. |
| PVC / vinyl | NEVER | "Vinyl" labeled. Sharp acrid smell. Damages tube + lungs. |
| Polystyrene (foam-core) | NEVER | Bright burn, toxic styrene fumes. |
| HDPE / Polyethylene | Avoid | Numbered "2" recycle. Melts unevenly. |
| Polypropylene | Avoid | Numbered "5" recycle. Melts. |
The plastic burn test (LAST RESORT: outdoors only)
- Take a tiny sample (1mm cube).
- Hold with metal tweezers OUTDOORS away from your face.
- Light briefly with a candle/lighter. WATCH, DON'T INHALE.
- Sweet smell + sooty smoke = polystyrene or polycarbonate.
- Sharp acrid sting in nose (immediately step away) = PVC. NEVER laser.
- Apple/citrus smell = polyethylene.
- Burning hair smell = wool / nylon (acceptable for some).
- This is a last-resort identification, better to ask the supplier or refuse the unknown material.
Leather: veg-tanned vs chrome-tanned
VEG-tanned: laser-safe. Chrome-tanned: TOXIC when burned. Tell them apart:
- Veg-tanned: light tan / honey colored when fresh; gets darker with age. Stiff. Smells "clean leather." Premium suppliers (Tandy, Wickett & Craig) label it.
- Chrome-tanned: often dyed dark from manufacturer (black, red, blue). More flexible/soft. Most fashion leather goods (handbags, jackets) are chrome-tanned. The "ick" smell when warmed is a giveaway.
- If you can't verify: assume chrome-tanned and don't laser.
Wood: laser-friendly vs problematic
- Birch ply, maple, cherry, walnut, basswood: all great. Laser-friendly.
- MDF: works but releases formaldehyde from the binder. Run extraction.
- Pine: resin pockets cause inconsistent burn. Spotty results.
- Oak / red oak: heavy grain overpowers detail. Engraves but inconsistent.
- Pressure-treated lumber: NEVER. Contains arsenic / chromium / copper compounds.
- Plywood with phenolic glue (cheap construction grade): burns hot, releases formaldehyde excessively.
Look for "laser-grade plywood" from suppliers like Ocooch Hardwoods or Bell Forest Products. Construction-grade plywood (Home Depot, Lowes) varies wildly in glue and quality.
The universal customer-question template
When a customer brings unknown material, ask:
- "Where did you get it?"
- "Do you have the original packaging or label?"
- "What's it made of?"
- "Has it been treated, painted, or coated?"
If you can't get satisfying answers, refuse the job. Better to lose a $50 customer than damage your laser or your lungs.