Thursday, March 19, 2009

Leather Furniture - Dyes or Pigments?

I am often asked to explain the difference between aniline dyed leather (unfinished) and protected or pigmented leather (finished) furniture. This post gives you the straight scoop between dyes and pigments as relates to leather furniture.

First, let’s cover some base-line information about leather to help you better understand its properties. Leather is a natural product. It comes from animal skins which have been chemically processed (tanned) to preserve them. A properly tanned hide (or skin) creates strong, flexible leather, resistant to decay.

Most leather upholstery found on furniture and in automobiles is tanned cow hide. Cow hides are about 1/4 to 3/8 inches thick, which is too heavy for general upholstery application. Therefore, hides are split laterally, rendering an upper and lower cut.

The upper portion is the top-grain, or full-grain. The lower portion is the split. This cutting process creates different “faces” to the leather. The outside face of the top- or full-grain shows the natural grain characteristics, but is otherwise smooth, whereas, the underside appears as suede.

There are two basic categories: Finished or Unfinished. Briefly, finished leather is first dyed via immersion in an aniline dye solution, and then the outside face of the hide is coated with a pigmented resin, and then a subsequent clear-coating. Unfinished leather processing stops at the first dyeing process, without any resin coating. Finished leather is protected by the color-coating and clear-coating, and unfinished is unprotected, not having either of these subsequent coatings applied.

The key point is the color you see on a finished leather is from a pigment coating on the leather, whereas unfinished leather color is a dye in the leather. Finished leather is stain and fade resistant but lacks deep richness in color, and tends to be stiffer. Unfinished leather is soft and natural-looking but fades and stains readily. Unfinished leather tends to be more expensive as only the finest, cleanest (fewer unsightly characteristics such as hide scars, branding marks, etc.) hides can qualify as unfinished.

This graphic depicts the difference between finished and unfinished.

Note that all cases (finished and unfinished) the leather is aniline dyed.

You can see that the topical coating can range from thin to thick. If there is a very light color or clear coat on top of aniline-dyed leather, it is often referred to as “semi-aniline.” Semi-aniline leather offers modest protection while retaining much of the aesthetic beauty of unfinished aniline-dyed leather. These are the arrtibutes of finished and unfinished leather furniture.

Finished: The leather has a topical pigment coat applied. One of the most common coatings consists of a soft acrylic color coating under a urethane clear coating (for durability). These resins create a film that bonds to the surface of the leather. Its primary goal is to protect the leather, providing wear, stain, and fade resistance.

Finished leather will resist staining by water- or oil-based agents (if a drop of water is put directly on the leather surface, the water bead remains on the surface, and does not soak in and darken the material). The clear coating determines the final reflective value of the leather surface (ranging from high gloss, to matte). Generally, finished leathers do not have that "buttery soft" leather feel (or hand) associated with raw leather. Also note, finished leathers can be described as aniline-dyed, and still have a topical pigment applied. Finished leathers are much less susceptible to fading

Unfinished: The leather does not have a topical pigment applied, or has a minimal resin coating to retain the hand of raw leather. The color is achieved by immersing hides in aniline dyes that are absorbed into the leather, accentuating the natural beauty of the hide. Because leather's absorption characteristics are not uniform, variations in color are common. The water drop test will result in the drop transferring into the leather, darkening or staining the area. Unfinished leathers are colored using organic aniline dyes which are highly susceptible to fading (caused by UV exposure).

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Copyright 2009 Kevin Gillan

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