There are two types of top grain leather available: corrected grain and full grain. Corrected grain leather refers to leather that has been altered by buffing its surface to reduce scarring or embossed to develop a special effect. Full grain leather, on the other hand, is left in its natural state; nothing has been done to alter its grain.
Because each cowhide comes from an individual cow, each hide has different markings on it that reflect the lifestyle and personality of that cow. These markings include scars from barbed-wire cuts and insect bites, brands, stretch marks from the birthing process, neck wrinkles, etc. The amount and extent of these markings determine the quality of a top grain cowhide.
A top grain cowhide with excessive scarring is less desirable than a cleaner cowhide because the scarring reduces the yield of the hide. To obtain a better yield, hides with excessive scarring are often buffed to reduce the amount of scarring. The buffing process is similar to sanding a piece of wood; it alters the grain by sanding it to a smooth surface. On some hides the entire surface will be buffed smooth then the grain will be printed back on the hide, which is called embossing. Other hides may only have random scars buffed out and the rest of the grain is left intact. Regardless of the amount of buffing, any hide whose grain is altered is referred to as a corrected grain.
The grain in full grain leather has not been altered. These hides have fewer scars, so it is unnecessary to alter their surface. Full grain hides are considered premium leather and are softer than corrected grain hides. Corrected grain leather is as durable as full grain leather, but the buffing process reduces the natural softness. Full grain hides are often used for the more expensive semi-aniline and aniline leathers. Keep in mind that full grain hides will have a mixture of loose cell structures and finer cell structure from various locations on the original hides. Hence, each hide is a unique combination of smooth and rougher texture as you might imagine.
Please note that some scarring is natural. One of the beauties of leather is that no two cowhides are alike, because each hide has different markings; therefore, no two leather sofas will be the same. Thus, there is no such thing as a perfect piece of leather; every piece of furniture upholstered in leather will have a few scars. These scars are not "defects" in the leather, but instead, genuine proof of its natural origin.