Tanning can leave leather stiff, dry, and rough—making it prone to cracking over time. That’s why it’s followed by an essential step in the leather-making process: the application of oils to soften, preserve, and enhance durability. This process, known as fatliquoring, typically takes place in a rotating drum, where the leather is treated with a fatliquor emulsion for even, efficient absorption.

At Tsuchiya Kaban, some of the leathers we use are treated with significantly higher amounts of emulsion to achieve the exact qualities we seek. For example, our signature Nume Leather—used to craft our Nume Collection—is treated with nearly three times the standard amount of emulsifier. This process gives the leather its distinct flexibility and soft, richly textured feel.

The emulsions themselves can include a blend of natural oils—such as castor, rapeseed, neatsfoot, lanolin, and fish oil—as well as petroleum-based and synthetic oils. Each emulsion blend is carefully selected to suit the characteristics of the leather and the intended finish.

Leather embossing is the process of pressing a heated metal mold onto leather under high pressure to imprint it with various designs or patterns. There are two main types of embossing: one mimics other materials—such as crocodile, snake, lizard, or ostrich skin—while the other enhances the leather itself with geometric patterns like lattices or organic textures such as wrinkles and natural grain.

Embossing adds beauty and depth to leather, but it demands a high level of craftsmanship—so much so that some workshops specialize exclusively in this technique. Today, embossed leathers that imitate reptile or ostrich textures have become so refined, they’re valued in their own right rather than seen as substitutes. Embossing the leather with Intricate patterns can also help conceal natural imperfections in the hide while protecting it from future scratches.

Leather milling is a process that softens the fibers of leather while enhancing its natural texture, such as wrinkles and grain. The leather is placed in a large rotating drum, where it is gently tumbled and kneaded to loosen the structure. Milling time varies depending on the type of hide and the desired finish, but typically ranges from 10 to 24 hours.

Milling softens the leather fibers, resulting in a supple, smooth touch and a richly textured appearance. Unlike shrinking (see below), milling does not contract the leather, which allows it to maintain a soft, natural finish. At Tsuchiya Kaban, the Tone Nume Collection's Soft Nume Leather and the Clarte Collection’s Field Soft Leather are prime examples of the soft, luxurious finish achieved through milling.

Shrinking is a process of treating leather with special chemicals and heat to contract its surface and enhance its natural grain texture. The resulting leather is referred to as shrink leather, and at Tsuchiya Kaban, it is featured in our Brent Collection.

While other leathers may appear similar—such as those textured through tumbling, hand-kneading, or embossed with wrinkle patterns—shrink leather is unique in that the leather itself is physically contracted. The result is a denser fiber structure and a firmer, more resilient texture.

A key characteristic of shrink leather is its ability to conceal natural imperfections such as scars, wrinkles, and vein marks, thanks to the way the grain emerges during the shrinking process. The resulting texture displays subtle variations in size and depth depending on the type of leather and the part of the hide used, giving each piece its own rich, individual character. The fine grain also helps make any new scratches less noticeable over time.

The process of eliminating natural texture from leather to achieve a sleek, glossy finish.
Leather with a smooth, even grain surface is known as smooth leather, as opposed to textured leathers such as embossed, brushed, or shrink-treated types. However, leather that has been artificially smoothed through film coating or enamel finishing is generally not classified as smooth leather.

Because leather naturally contains subtle irregularities—such as scars, wrinkles, and grain variations—achieving a truly smooth finish requires additional processing.

Common smoothing techniques include hot pressing with a large heated metal plate, and glazing, where a hard agate ball is rolled and pressed firmly over the surface. Glazing not only smooths the leather but also adds a transparent, lustrous shine, making it a preferred method for finishing premium leathers like cordovan.

Nume leather, as it’s known and favored in Japan, widely refers to a category of leathers that are tanned with vegetable or synthetic tannins.

Nume leather is one of the oldest and most traditional types of leather—an ideal choice for those who appreciate the natural beauty of leather, especially in its unique markings, such as wrinkles, veins, and the occasional scratch. Its most defining feature is the way it develops a rich patina over time, deepening in color and character with use. Lighter shades are especially popular for their dramatic and visible transformation.

While the exact origin of the term “nume” is unclear, some believe it comes from the Japanese word 滑 (nume), meaning “smooth,” a nod to its silky feel.