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 Surface Colorants |
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| Prior to World War II, leathers produced were solely vat dyed. Colors were dark and limited in number. Usually these colors faded quickly and developed into strange shades of greens or browns after exposure to the sun. Although the surfaces did not crack and chip as badly, the leather still became dry and stiff. |
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After the war, new technology created new demands and brighter colors quickly became popular with the availability of nitrocellulose lacquers. Leather finishes were limited in color only by imagination and taste (or lack thereof). Leathers that were vat dyed were now surface coated as well. In the early 1980’s nitrocellulose lacquers gave way to the resin-base dyes in use
today. |
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| If your vehicle predates the 1980’s and nitrocellulose lacquers were used in dying the leather, here is what’s happening to the surface: Nitrocellulose lacquers were brittle surface colorants generally used on the exterior metal surface of the automobile body. Flexing agents or plasticizers were added to keep them from cracking. The coloring of leather required additional plasticizers for added flexibility. There was a delicate balance which had to be maintained. Although the addition of plasticizers increased the flexibility of the lacquer, the durability decreased. The surface became more subject to wear and abrasion, and the actual adhesion of the lacquer to the leather diminished. It loosened where flexed and chipped away. |
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| Additionally, since these colors were generally sprayed on the surface, they were further reduced with thinners for even application. The actual thickness of the lacquer finish was extremely thin. Thicker applications would create a loss of suppleness and inhibit the leather’s ability to “breathe.” |
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| Plasticizers were also unstable; they underwent a chemical change and migrated into the atmosphere — or, quite simply, disappeared. What remained on the leather surface was a stiff, brittle, non-porous coating, which in itself is bad enough. However, it further restricted the ability of the leather to flex and breathe, and actually accelerated the deterioration process. Once begun, this aging process progressed more and more rapidly. So ends the story of nitrocellulose lacquer colorants. |
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| If old leather is not used for long periods of time, a sudden flexing will sometimes result in actual cracking like folding old, dry cardboard. Old seats have actually been known to “shatter” when pressed or sat upon. |
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| Other things are also happening to the leather. Recall those oils that were added during the fatliquoring finishing process? Well, they migrate as well! The omnidirectional fibers which were once plump and flexible are becoming thinner and more rigid. Instead of flexing and stretching with use, the fibers are getting tight and compact and tend to tear when stretched. Like bending a piece of metal repeatedly in the same place, the structure weakens and the metal breaks. This same process is happening in these “wear creases” in the color finish of leather; the leather eventually weakens in these flexed areas and separates. Instead of a surface crack, there is now an actual split in the leather. |
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| Depending on climate, storage and use, this deterioration process can happen in as little as two years. |
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