Guaged
Guaged refers to a process where the thickness of a series of tiles is evened out for the installation process. If stones have varying dimensions, they may set unevenly in an architectural application. The way to resolve such a problem is to use mechanical grinder to remove excess stone from each tile.
Natural / Cleft
When slate has a natural clefted finish it means that the surface of the stone is rough, and has not been honed or polished down. The word “cleft” refers to the splitting that occurs within the stone, during its formation, and which causes the uneven features found in finished tiles.
The main draw of using clefted slate is that it has a natural and rustic look. Cleft stone looks like real stone, and it gives an application an “outdoorsy” feel.
Another major advantage of using clefted material is that it is extremely slip resistant. That is why many restaurants and commercial kitchens use this material, as it cuts down on lawsuits from customers who fall in wet puddles.
Clefted material also tends to wear down well in high traffic areas. The dimensional nature of the stone tends to soften over time, and achieves an attractive brushed patina which many people find to be quite beautiful.
The drawback to using a clefted material is that it may be uncomfortable to walk on it with bear feet, due to the tiny ridges and peaks which poke out of its surface.
Polished
Slate that has been polished has been grinded by a machine to give the material a smooth, shining, glossy appearance. Polished slate tends to resemble marble, except that the colors are more unique, and the dimensionality that was in the original stone is retained to a certain extent, as shadow lines in the polished surface of the material.
Polished slate is often considered more elegant than natural slate, and has a more “finished” look. It also tends to retain many of the colors and features found in the original stone, making it both rustic and powerful, while still retaining its sophistication and style.
The problem with polished slate is that it is never as dramatic as the natural surface of the stone, and many of the powerful colors found within it will be washed out by this process. Polished slate is also quite slippery, and doesn’t have any of the dimensional qualities that make the clefted version so popular in restaurants.
The polished version will also tend to show scratches and dirt much more easily than a natural finish will.
Honed
A honed finish is the halfway point between clefted and polished slate. A honed surface is smooth to the touch, but doesn’t have the glossy shiny appearance and texture that a polished material has.
A honed finish is generally used when you want a polished look, but you don’t want material that will cause a slipping hazard. This type of finish gives slate a little bit of texture, just enough to catch your shoes on, making it much safer than a polished alternative.
Unfortunately you do lose many of the colors and features found in a natural stone when you hone it, making the outcome considerably less vibrant.
Brushed / Flamed
The brushed or flamed finish is relatively new in natural stone. It is a process where a natural cleft is honed down slightly, just enough to get rid of the most dramatic peaks. The difference between this and honing is that the resultant materials looks like it is natural, with the vibrant colors and the dimensionality, but you can walk on it with bear feet.
Brushed material is very popular in hotel lobbies where owners are trying to achieve a look which is both dramatic and inviting, without presenting a slipping hazard, and without the natural clefting that can make people walking in socks uncomfortable.
Conclusion
There are many different choices you have for the finish of your natural slate. The style you choose should depend largely on taste, but also on the application you are trying to achieve. You have to balance slip resistance and color against uniformity and elegance, and figure out what is really important in your project.