Book care basics: foxing, mould, and safe storage

Foxing is the name for the small reddish-brown spots that appear on older paper. It is generally an age-and-humidity effect in the paper itself, is usually stable, and does not spread from book to book. Mould is different: it is a living growth, often fuzzy or with a musty smell, and it can spread and damage paper and bindings. If a mark is flat, rusty-brown, and confined to the page, it is more likely foxing; if it is raised, fuzzy, green/black/white, or smells musty, treat it as possible mould.

Distinguishing the two by eye is not always possible, and this guide cannot diagnose a specific book. When in doubt, treat a suspect book as possibly mouldy and keep it away from the rest of your shelves until you know more.

For active mould, insect damage, or a book that has been wet, the safest first step is to isolate the book and reduce the humidity around it, then seek professional advice. Do not apply household bleach, solvents, or other chemical treatments to a book — these can cause irreversible damage, and the corpus of collector advice is full of well-meant home remedies that made things worse. A conservator or your local library or archive can advise on safe handling.

• American Institute for Conservation — find a conservator ↗

• Keep books out of direct sunlight — UV fades spines and jackets over time.
• Aim for a stable, moderate temperature and humidity; damp basements and hot attics are the two hardest places on a book.
• Shelve books upright and reasonably snug so they support each other, and store very large or heavy books flat.
• Give shelves some air circulation and avoid pressing books against a cold external wall where condensation can form.

These are general good-practice basics, not conservation-grade instructions. A book of real sentimental or financial importance deserves a conversation with a professional conservator.