What would be the most common cause of deterioration to the 15th century book?

The most common cause of deterioration to a 15th-century book would be natural aging, as these books are susceptible to various factors over time. Some specific causes of deterioration include:

1. Environmental factors: Exposure to high humidity or fluctuations in temperature can cause the paper to become brittle, moldy, or warped. Sunlight can also fade the ink and weaken the binding over time.

2. Insects and pests: Books can be damaged by insects like bookworms, silverfish, termites, or mice, which may burrow into the pages or cover, leaving behind holes, nibbled edges, or droppings.

3. Poor handling and storage: Incorrect handling, such as forcefully turning pages, mishandling the spine, or storing the book in improper conditions, can lead to tears, spine damage, or loosening of the binding.

4. Acidic paper: Many books from the 15th century were printed on paper made using acidic materials. Over time, this acidity can cause the paper to yellow, become brittle, or disintegrate.

5. Water damage: Exposure to water, moisture, or flooding can cause the pages to warp, smudge or even dissolve the ink, leading to illegible text or images.

6. Inadequate cleaning practices: Improper cleaning methods, like using adhesive tapes, abrasive materials, or harmful chemicals, can cause irreversible damage to the delicate pages or binding of a book.

7. Inherent weaknesses: Books from this period may have inherent weaknesses due to the quality of materials used, such as weak spines, delicate or easily torn pages, or weak bindings that can deteriorate over time.

To preserve and protect a 15th-century book, it is essential to store it in a stable environment with controlled temperature and humidity, handle it carefully with clean hands, and consult conservation professionals for any restoration or conservation needs.