Marble or Granite for photo engraving?

By Mike Wallis 

In this article we'll take a look and some of the characteristics of both marble and granite and what roles they play in laser photo engraving. The purpose of this analysis is to possibly help determine which stone is better used for a given application.

Black marble and granite is the preferred stone for photo engraving in the laser engraving industry. This is mainly due to the contrast capabilities. Starting with a dark color stone is the best way to achieve a high contrast without a color fill. When laser engraved correctly it should produce a white or gray mark. The white/gray mark overlayed against the black marble or granite will result in a black and white photo engraving. Because of the popularity of the color for laser engraving and the high contrast characteristics, only black marble and granite will be covered for the scope of this article.

Marble (Black)

Granite (Black)

Definition - Marble is a non-foliated
metamorphic rock composed of re crystallized carbonate minerals, most commonly calcite or dolomite.

Hardness - (3) on the hardness scale. Soft

Fossils/Veins - high

Definition - Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granites usually have a fine, medium or coarse grained texture. 

Hardness - (7) on the hardness scale. Hard

Fossils/Veins - medium

Location - ( Interior or Exterior)

The first and usually most important question to ask before determining between marble or granite for photo engraving is "Where will the stone or plaque be located". If it's going to be located inside out of the elements then either one will fit the application. On the other hand if the piece needs to be placed outside then granite is the hands down choice. Granite has a hardness of seven on the moh's scale which puts it not to far below diamonds which is at ten. This makes it ideal to for exterior applications because it is less susceptible to abrasion. Because of the high durability of granite monument companies have almost exclusively chosen granite for cemetery headstones and other exterior applications. Marble has a hardness of three which means that it will weather significantly quicker outside compared to granite.

Scratch Resistance

Another important factor to consider is whether or not the item will need to be scratch resistance. If placement is on a table top, a wall, behind a glass case or somewhere where contact with the piece will be low, then being scratch resistance is not a needed feature. On the other hand if it's to be placed in areas where abrasion is likely then this is just as important to consider as interior or exterior placement. Abrasion areas might include flooring, high traffic areas and public halls to name a few.
As outlined above marble is a softer stone which makes it more likely to be scratched when placed in those areas prone to abrasion. Because of this soft characteristic of marble it's not recommended for these type of applications.
Granite however is well suited for high traffic areas and can even be used as flooring. The main enemy's of granite in high traffic areas or the photo engraving on it is the possibility of graffiti. Though the polished surface of the granite can be restored, once painted it would be difficult (not impossible) to remove it from the etched portions. A strong chemical such as lacquer thinner would be a good candidate to remove the paint and would not damage the surface.

Will Water Damage Marble or Granite?

Will water hurt black marble? Yes, in a big way. Because of it's softness the water will quickly etch away at the surface. Will water hurt granite? No and yes. Regular rain fall will NOT damage granite unless of course it's acid rain. On the other hand water that is hard or contains high levels of calcium or chlorine can wreak havoc on it. As the water hits the surface on a regular basis the minerals build up and are extremely difficult to remove. This type of damaging water mostly comes from sprinklers and the water supplied from city water systems. To avoid water mineral damage always place the granite out of reach of sprinkler systems.

Detail

One of the biggest questions I get from customers when it comes to choosing between granite and marble for photo engraving is "Which one engraves with better detail?". Although the are close marble tends to have a slightly higher detail when engraved over granite.

Fossils and veins

Fossils and veins in marble and granite is probably one of the biggest things to consider. A fossil bug or white vein going across someone's face on a engraved photo will quickly turn into a major eye sore. Almost all black marble has some degree of veining, some wide veins and others hair line veins. Even if you don't see veining on the polished surface turn it over and look on the back, when you do your likely to see some veining which may or may not show in the engraved picture. The key to minimize the veining from showing up in the picture is to cut around the veins. Black granite rarely has veining and is usually not a issue. Both marble and granite will have some form of fossiling. Fossils are inconsistencies in the stone like an unusual gray spot or a cluster. Most of the time the fossils are visible by looking at the surface. This visual give away helps so that you can have the opportunity to select another piece before it's go through someone's forehead in the photo.

Conclusion

Marble and granite are both excellent for laser photo engraving but careful consideration should be made before selecting. For outside applications and where durability is a must granite should be selected over marble. Also taking time to look closely at the piece before engraving will prevent unwanted fossils from showing up in the granite or marble photo.

We use only the highest quality marble and granite for laser photo engraving with minimal veining and the smallest possible grain size. Click here to view our products and submit for your free proof.