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Surface Finishing

Surface finishing is the treatment that brings out the esthetic features of the material. The ornamental function and also some technical characteristics (e.g., its resistance to wear and to weather conditions or its slipperiness) are strongly influenced by the surface finishing applied to the product. Depending on the treatment, we can divide the finishing into mechanical, impact, and chemical methods.

 

Mechanical Finishing:  In mechanical finishing, the stone is put in contact with an abrasive to reduce the original surface roughness to some extent.

Sawn Finish
Though infrequent, sometimes the sawn material or even just-quarried material is ready for installation and needs only to be cut to size. The surface in this case is generally rough, with an uneven face. Rough stone is predominantly used outdoors, where it is appreciated for its non-slip quality. It is often used with slate and with some kinds of sandstone.

Honed Finish
This finishing aims to produce a smooth surface by using abrasives of ever finer grain on the surface, so there is not a single honing but a series of progressive degrees of it. The surface quality of honed stone depends on the last grade of abrasive applied, and therefore the finish gets its name from it (honed 140, honed 200, honed 400, etc.). Honed finish is not reflective and makes the color tones slightly dull, but the treatment preserves the material's natural esthetic characteristics.

Polished Finish
Polishing is the main and the most frequently applied finish. It follows the finest honing and employs polishing abrasives that add brilliance with mirror effect to the stone surface.

 

Impact Finishing:  In impact finishing a strong external force is applied to the stone surface in order to alter and enhance the original surface roughness. Because they produce surface unevenness, these finishes are usually not slippery, but they do get dirty easily.

Brushed Finish
Brushed finish is obtained by applying hard plastic or metal brushes to the stone surface. The heavy action removes the softer part of the stone and wears out the surface, giving it a look similar to that of antique finishing.

Bush Hammered Finish
Bush Hammering is obtained by hitting the material surface mechanically or by hand with a specific multipointed tool. This method creates a rugged surface full of little grazes at the impact points, and it modifies the color, making it lighter. The surface becomes non-slip. This technique has been replaced by flaming and pressure water finishing because these are faster and less costly.

Tooled Finish
Tooling is similar to bush hammering but it is obtained with a larger, single-pointed steel tool. The chromatic and non-slip effects are similar to those obtained with bush hammering, but tooling can be applied only to a chosen part of the surface, thus leaving some rough areas. The effect it produces is useful in giving stone a medieval character.

Sandblasted Finish
In sandblasting, a high-pressure jet of siliceous sand or carborundum or steel shots is applied to the area to be treated. It produces a smooth abrasion, leaving the material slightly scratched on the surface, but not rugged. The color tones and the veins are a bit dulled.

Flamed Finish
Also called thermal finishing, flaming consists of passing a blowpipe that emits a high-temperature flame over the surface to be treated. The heat acts by blowing the crystals out as they suffer thermal shock with an effect that is particularly evident in materials composed of minerals with various degrees of expansion e.g., the vast majority of granites. The surface produced is rough and non-slip, and the color is generally faded hiding defects and tone variations. Because of oxidation, yellow materials become orange or red

Water Finish
This process consists of passing a pipe emitting a jet of high-pressure water over the surface to be treated. The effect is the negative of what happens with thermal finishing. While with flaming the hardest part of the material bursts and is removed, in water finishing and softest part is removed. But the result looks the same: the surface is similarly rough. For this reason, water finishing is incorrectly called "water flaming." The colors of the material and the veining pattern are not affected by water finishing and the esthetic effects are comparable even to those obtained by polishing. As water finishing does not induce oxidation, it is the usual finish employed for making yellow materials non-slip.

Antique Finish
Special machinery that looks like industrial washing machines is used to obtain an antique finish. The pieces to be treated are put in the machine with abrasive elements and the cylinder revolves. In a short time the impact of the stone with the abrasives produces an effect similar to aging caused by use and wear. The impact method is not suitable for large pieces, for which brushing or acid washing is the method of choice.

Split Finish
A split finish is obtained by hitting a small block of stone with a metal wedge. If the splitting is performed along the lines of cleavage planes in materials with well-defined parallel layers (e.g., slate), a rather smooth and uniform surface is produced. It is also possible to split other materials, causing a crack that divides the small block in the middle. This is a very stressful finish for the stone, and the surface obtained is extremely rugged. It is not possible to perform it on large pieces that would resist the break.

 

Chemical Finishing:  Chemical finishes are applied to stone in order to produce reactions that transform the material surface, or they are employed together with other types of treatment in order to improve their characteristics. These finishes can also be applied to cut, or even installed, materials.

 
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