| Anodized Aluminum:
Anodized aluminum comes in a variety of colors and can usually be engraved with a CO2 laser. Black anodized aluminum is great to work with because it turns white when lasered. It provides the best contrast of all colors. Some colors, red for instance, do not turn completely white when laser engraved. Red anodized aluminum, when lasered, produces a light pink color. Although some improvement can be seen by performing a second pass, usually a slight hint of pink will remain. Remember to engrave anodized aluminum at high speeds and low powers for crisp, clean images. Too much power applied to the anodize will distort the engraving and tends to over-burn the image.
While uncoated brass cannot be laser engraved, you can still achieve an excellent product by utilizing brass that has some sort of coating, typically paint. The laser removes the coating and exposes the brass substrate.
By far, the most popular laser engravable brass is brass-coated steel. First, a steel substrate is coated with a thin layer of brass. Next, the brass is polished to a reflective finish and a coat of lacquer is applied to the brass. Finally, a paint coating is applied on top of the lacquer for the finished product.
When laser engraving brass-coated steel, you are removing only the paint and exposing the polished brass coating that is protected by the lacquer. The lacquer prevents the brass from oxidizing and the bright reflective surface will stay bright for years. If you are unsure if the piece that you have is either brass or brass-coated steel, you can test the material with a magnet. A magnet will stick readily to brass-coated steel. Since solid brass is not magnetic, a magnet will fall away from solid brass.
In order to engrave on bare metal, you'll need a laser engraver with a minimum of 25 watts and utilize a metal marking spray such as Cermark.