The "Stainability" of Natural Stone
Whether or not a natural stone will stain is something that many people wonder about when trying to choose which type of stone to use in the home. Even if you have chosen which kind of stone you want, you may still contemplate whether it will stain easily. This article expalin what things to consider when determining how "stainable" your stone will be.
The Stone's Properties Are Important
When trying to determine how easily your natural stone surface will "stain", the first thing to know about the material is its properties. What the stone is called is not the important thing. In the stone industry, the same "label" or "classification" can be given to stones that are very different in composition and structure. So, if the name of the material is not the important factor, then what does matter?
The properties of the material affect it's vulnerability to what many refer to as staining (although some discolorations are not stains at all). We will briefly look at two properties that can impact how easily natural stone can discolor. The first is the density of the stone and the second is the mineral content.
Density and Absorption
The density of the stone impacts how easily it can "stain". If the stone is porous, it allows liquids to soak into the material. If the liquid has color, when it penetrates to pores of the stone, it can discolor (or stain) the material.
The porosity of stones vary. Even two stones with the same label or classification can have porosity that varies. The variance in the stone's density affects the rate at which it will absorb liquid. As a general rule, the higher the density, the more stain resistant the stone.
This means that knowing how dense your material is will give you an idea of its ability to stain. Therefore, knowing this is key. Testing the absorption rate will indicate how dense a particular stone is. This can be done by putting water o the surface of the stone and timing the absorption. This is sometimes called "doing a water test".
Another property that can affect how easily your stone surface will discolor or "stain" is the mineral content. Often times certain kinds of stone will contain a mineral called calcite. As mentioned on Calcite's Wikipedia page, certain substances will dissolve calcite. Regarding this Wikipedia states:
Calcite, like most carbonates, will dissolve with most forms of acid.
That means certain household liquids (including some foods) can dissolve the calcite in stone. Calcite is also what gives the stone a luster (a natural glow or sheen). When this mineral is dissolved, the luster is lost and a dull spot appears. This dull spot is known as "etching". Since and etch is a discoloration in stone it sometimes is misconstrued and is referred to as a "stain". So technically, etching is not a stain. However, some may think it is a stain. It is a discoloration, so it makes sense to consider it when discussing stains - even though it actually is not.
Just as there are ways to test the density of a material, there are ways to test the mineral content. Using what is sometimes called an "acid test", you can determine if your stone is composed of calcite. Use a small inconspicuous area of the stone or do this test on a sample of the material. Place a small amount of an acidic liquid (lemon juice, vinegar, etc.) wait a couple of minutes for the reaction to happen. Then, wipe up the liquid and check for a dull spot. The presence of a dull spot means that you probably have a stone composed of calcite.
So in summary, the density of your stone and the minerals with in it can affect its resistance to discoloration. There are ways of testing these properties. And if you do end up with a stone discoloration whether its is an etch or a stain, There are methods that might help to correct the blemish. However, knowing the properties of the stone beforehand can help you to protect your stone surfaces before staining becomes an issue that needs corrected.