Editing Laser engraving (section)

==Materials that can be engraved==

=== Natural materials ===
The marking of organic materials like wood is based on material carbonisation which produces darkening of the surface and marks with high contrast. Directly "burning" images on [[wood]] were some of the first uses of engraving lasers. The laser power required here is often less than 10 [[watt]]s depending on the laser being used as most are different. [[Hardwood]]s like walnut, mahogany and maple produce good results. [[Softwood]]s can be judiciously engraved but tend to vaporise at less-consistent depths. Marking softwood requires the lowest power levels and enables the fastest cut speeds, while [[active cooling]] (e.g. a fan with sufficient airflow) inhibits ignition. Hard papers and fiberboard work well; linty papers and newsprint are like softwoods. Fur is not engraveable; finished leathers though can be laser-engraved with a look very similar to hot-branding. Certain [[latex]] rubber compounds can be laser engraved; for example these can be used to [[fabrication (metal)|fabricate]] inking-stamps.

Paper [[masking tape]] is sometimes used as a pre-engraving overcoat on finished and [[resin]]y woods so that cleanup is a matter of picking the tape off and out of the unengraved areas, which is easier than removing the sticky and smoky surround "halos" (and requires no [[varnish]]-removing chemicals).

===Plastics===
Each plastic has specific material properties, especially the light absorption spectrum. The laser irradiation can generate direct chemical modifications, melting or evaporation of the material. Plastics are rarely seen in their pure state because several additives are used such as colorants, ultraviolet retardants, release agents, etc. These additives impact the result of laser marking.

Standard cast [[Polymethyl methacrylate|acrylic plastic]], acrylic plastic sheet, and other cast resins generally laser very well. A commonly engraved award is a cast acrylic shape designed to be lasered from the back side. [[Styrene]] (as in [[CD|compact disc]] cases) and many of the [[thermoforming]] plastics will tend to [[melt (manufacturing)|melt]] around the edge of the engraving spot. The result is usually "soft" and has no "etch" contrast. The surface may actually deform or "ripple" at the lip areas. In some applications this is acceptable; for example date markings on 2-litre soda bottles do not need to be sharp.

For signage and face plates, etc., special laser-marked plastics were developed. These incorporate [[silicate]] or other materials which [[Conduction (heat)|conduct]] excess heat away from the material before it can deform. Outer [[laminate]]s of this material vaporise easily to expose different coloured material below.

Other plastics may be successfully engraved, but orderly experimentation on a sample piece is recommended. [[Bakelite]] is said to be easily laser-engraved; some hard engineering plastics work well. Expanded plastics, [[foam]]s and [[Polyvinyl chloride|vinyl]]s, however, are generally candidates for routing rather than laser engraving.  Plastics with a chlorine content (such as [[Polyvinyl chloride|vinyl]], PVC) produce corrosive chlorine gas when lasered, which combines with Hydrogen in the air to produce vaporised [[hydrochloric acid]] which can damage a laser engraving system. [[polyurethane|Urethane]] and [[silicone]] plastics usually do not work well, unless it is a formulation filled with [[cellulose]], stone or some other stable [[Thermal insulation|insulator]] material.

[[Kevlar]] can be laser-engraved and laser-cut. However, Kevlar does give off extremely hazardous fumes ([[cyanide]] gas) when it is vaporised.

===Metals===
Metals are heat resistant and thermally conductive, making them more difficult to engrave than other materials. Due to their thermal conductivity, pulsed, rather than continuous wave lasers, are preferred in laser engraving applications. High peak power, low pulse duration lasers are able to ablate material off a metal engraving surface without delivering enough energy to melt the surface.

[[File:Laserengravingonsteel.jpg|thumb|Laser on stainless steel]]

Metals can not be easily be engraved with common 10,600{{nbsp}}nm<ref>{{Cite web |date=2024-01-16 |title=Laser Engraving on Metal {{!}} Expert Guide |url=https://www.digthisout.com/laser-engraving-on-metal-expert-guide/ |access-date=2024-01-16 |language=en-US}}</ref> wavelength {{chem|C|O|2}} lasers, on account of many metals having high reflectivity around this wavelength. Yb:Fiber Lasers, Nd:YVO{{sub|4}}, both emitting light of approximately 1000{{nbsp}}nm wavelength, [[Nd:YAG lasers]] at 1,064{{nbsp}}nm wavelength, or its harmonics at 532 and 355{{nbsp}}nm, emit light that is more readily absorbed by most metals. They are thus more suitable for the laser engraving of metals.

===Coated metals===
The same conduction that works against the spot vaporisation of metal is an asset if the objective is to vaporise some other coating away from the metal. Laser engraving metal plates are manufactured with a finely polished metal, coated with an [[enamel paint]] made to be "burned off". At levels of 10 to 30 watts, excellent engravings are made as the enamel is removed quite cleanly. Much laser engraving is sold as exposed brass or [[silver]]-coated [[steel]] lettering on a black or dark-enamelled background. A wide variety of finishes are now available, including screen-printed [[marble]] effects on the enamel.

Anodized aluminum is commonly engraved or etched with {{CO2}} laser machines. With power less than 40W this metal can easily be engraved with clean, impressive detail. The laser bleaches the color exposing the white or silver aluminum substrate. Although it comes in various colors, laser engraving black anodized aluminum provides the best contrast of all colors. Unlike most materials engraving anodize aluminum does not leave any smoke or residue.

Spray coatings can be obtained for the specific use of laser engraving metals, these sprays apply a coating that is visible to the laser light which fuses the coating to the substrate where the laser passed over. Typically, these sprays can also be used to engrave other optically invisible or reflective substances such as glass and are available in a variety of colours.<ref>{{cite web|url=http://www.thermark.com/content/view/16/86/ |archive-url=https://web.archive.org/web/20080517151038/http://www.thermark.com/content/view/16/86/ |url-status=dead |archive-date=17 May 2008 |title=TherMark Laser Marking - How It Works |publisher=Thermark.com |access-date=2012-11-07}} </ref> Besides spray coatings, some laser-markable metals come pre-coated for imaging. Products such as this transform the surface of the metal to a different color (often black, brown or grey).

===Stone and glass===
[[File:Laser engraved glass microscope slide magnified.jpg|thumb|alt=Laser engraved glass microscope slide at 40x and 100x magnification.|Laser engraved glass microscope slide with the word "glass" engraved in 3pt font. Magnified to 40x and 100x]]
[[File:Wine glass fill line.jpg|thumb|right|A wine glass with a laser-engraved [[fill line]].]]

[[Rock (geology)|Stone]] and [[glass]] do not vaporise or melt easily. As a result, this makes them generally a better candidate for other means of engraving, most notably [[sandblasting]] or cutting using [[diamond tool|diamond]]s and [[water jet cutter|water]]. However, when a laser hits glass or stone, it fractures. [[Porosity|Pore]]s in the surface expose natural [[grain]]s and crystalline "stubs" which, when heated very quickly, can separate a microscopic sized "chip" from the surface because the hot piece is expanding relative to its surroundings.<ref>{{Cite web |date=2019-08-29 |title=Glass Laser Engraving & Etching – All You Need to Know |url=https://all3dp.com/2/glass-laser-engraving-etching-all-you-need-to-know/ |access-date=2022-05-31 |website=All3DP |language=en}}</ref><ref>{{cite journal
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 }}</ref> One should avoid large "fill" areas in glass engraving because the results across an expanse tend to be uneven; the glass ablation simply cannot be depended on for visual consistency, which may be a disadvantage or an advantage depending on the circumstances and the desired effect. {{As of|2021}}, recent advances in UV laser technology now supply 10W (or greater) of UV lasing energy and produce significantly better engraving results on glass than prior, lower powered iterations of UV laser marking systems (i.e. 3W) or classic {{CO2}} laser marking systems. The newer UV systems engrave cleanly and clearly without a high degree of micro-fracturing on the mark surface. Since modern 10W UV laser systems heat the surrounding substrate less than other laser marking systems, glass substrates are significantly less prone to fracturing from the laser marking process. High quality fill engravings on thin glass and crystal substrates are now regularly reproducible<ref>{{Cite web |date=2015-09-22 |title=Laser Marking on Glass: How to Achieve High Quality |url=https://www.findlight.net/blog/2015/09/22/laser-marking-on-glass/ |access-date=2022-05-31 |website=FindLight Blog |language=en-US}}</ref> at high-volume in full production environments.