Exposure to noxious gases can also cause tendering. In some cases, these gases are converted to acids, which are the main cause for the deterioration of some textiles. Fibers that compose a fabric should be identified before any treatment is undertaken, particularly if stain removal is required. Physical tests, such as burning, quickly identify the presence of animal fibers, which do not burn readily and shrivel into a residue of carbon. These fibers usually emit the distinct odor of singed hair.
Vegetal fibers burn easily to a fine ash.
Many fibers and hairs can also be readily identified by microscopic examination. Animal hairs, for example, can be identified by their characteristic cuticle patterns and medullar cross sections. Simple staining tests enable the conservator to distinguish between the different kinds of fibers. The textile materials encountered most often in archaeological sites are linen, cotton, wool, and silk. Linen is a spun and woven vegetable-based fiber derived from flax stalks and branches.