Apart from being Jewish sacred objects, the 'tefillin' and 'mezuzot' are outstanding examples of the crafts. They are made of fine material, and each stage of the production takes a long time and requires special attention. Every part is symbolic and has a special meaning. 'Tefillin' and 'mezuzot' demand special care and environmental conditions. Their main enemies are water, dampness, sunlight, heat, microbes and insects, as well as mechanical factors causing damage during use. Since they are often and easily damaged, they are subjected to restoration. Conservation and restoration should be consulted with rabbis owing to the fact that only material from 'clean' animals can be used; each element should be preserved without any change to its original symbolic and significant form.