How to Store Rare Books — Temperature, Humidity, Light, and Shelving

The enemies of rare books are predictable: humidity, heat, light, pests, pollution, and physical mishandling. Of these, environmental storage conditions — temperature, humidity, and light — are the most important and the most controllable. A book stored in proper conditions for a century will remain in better shape than a book stored in poor conditions for a decade. The investment in proper storage pays compound returns in preservation.

Temperature

The Ideal Range

65–70°F (18–21°C) is the generally recommended temperature for book storage. Within this range:

• Chemical degradation (acid hydrolysis, oxidation) proceeds at a manageable rate
• Biological activity (mold, insects) is suppressed
• Paper and binding materials remain stable and flexible

Why Temperature Matters

Chemical reactions that degrade paper approximately double in rate for every 18°F (10°C) increase in temperature. This means a book stored at 86°F (30°C) degrades roughly twice as fast as one stored at 68°F (20°C).

Stability Is More Important Than Perfection

Moderate, stable temperatures are better than optimal but fluctuating temperatures. Rapid temperature changes cause materials to expand and contract at different rates, stressing bindings, cracking leather, and promoting condensation on cool surfaces.

Cold Storage

For extremely valuable or deteriorating material (nitrate film, color photographs, acidic paper), cold storage at 35–50°F (2–10°C) dramatically slows degradation. However, cold storage requires careful humidity control and gradual acclimatization when removing items for use.

Humidity

The Ideal Range

45–55% relative humidity (RH) is the recommended range for book storage. This is the single most important environmental parameter:

Below 30% RH — paper becomes brittle, leather dries and cracks, adhesives fail, and vellum warps and buckles.

Above 65% RH — mold growth becomes likely, foxing accelerates, insect activity increases, and adhesives soften.

Measuring Humidity

A hygrometer (humidity meter) is essential equipment for any serious collection. Digital hygrometers are inexpensive ($10–$30) and provide continuous readouts. Place hygrometers at book-shelf level, not on the floor or ceiling, for accurate readings.

Controlling Humidity

Dehumidifiers — in climates or seasons with high humidity, a dehumidifier is the most effective tool. Modern units can be set to maintain a target humidity level.

Humidifiers — in dry climates or heated winter environments, a humidifier prevents paper from becoming brittle.

Air conditioning — central air conditioning both cools and dehumidifies, making it effective for summer book preservation.

Desiccants — silica gel packets placed in enclosed bookcases help buffer humidity fluctuations in small spaces.

Avoid microclimates — books stored against exterior walls, near windows, in basements, or in attics experience temperature and humidity extremes that differ significantly from the room’s ambient conditions.

Light

UV Damage

Ultraviolet (UV) light is the most damaging wavelength for paper and binding materials. UV exposure causes:

• Paper yellowing and embrittlement
• Fading of inks, pigments, and dyes
• Deterioration of dust jacket colors
• Photochemical degradation of leather

Visible Light

Even visible light causes cumulative damage over time, though at a lower rate than UV. All light exposure is additive — damage accumulates with each hour of exposure.

Prevention

No direct sunlight — never store books where direct sunlight falls on them, even briefly. A book displayed in a sunny window can fade visibly within months.

UV-filtering glass — if books are displayed in cases near windows, use UV-filtering glass or acrylic in the case and on the windows.

Low-intensity lighting — use low-level incandescent or LED lighting. LED lights emit very little UV and are the best choice for book storage areas. Avoid fluorescent lights, which emit significant UV.

Lights off — when you are not actively using or enjoying the space, turn the lights off. This simple practice dramatically reduces cumulative light exposure.

Display Considerations

Books displayed in open cases or on shelves receive continuous light exposure. For valuable items:

• Rotate displayed books periodically (every few months)
• Display facsimile dust jackets and store the originals in the dark
• Use closed bookcases with solid (not glass) doors for the most valuable items

Shelving

Proper Shelving Materials

Metal shelving is preferred for rare book storage:

• Powder-coated or baked-enamel steel is chemically inert
• Will not emit volatile acids
• Resistant to pests

Wood shelving can off-gas volatile organic compounds (particularly formaldehyde from plywood and particle board) that accelerate paper degradation. If using wood shelving:

• Use solid hardwood, not particle board or MDF
• Seal all surfaces with a polyurethane or lacquer finish
• Line shelves with acid-free board or Mylar as a barrier

Shelving Practices

Upright shelving — most books should be shelved upright, with the spines vertical and the books supported by bookends or neighboring books.

Folio and oversize books — books taller than approximately 14 inches should be shelved flat (on their sides) to prevent the text block from pulling away from the binding under its own weight. Stack no more than two or three flat books together.

Not too tight — books packed tightly on shelves suffer abrasion damage when pulled out. Leave enough space to remove and replace books without friction.

Not too loose — books without adequate support lean, causing the text block to warp and pull away from the spine. Use bookends.

Spine out — always shelve books with the spine facing outward. Never shelve books with the fore-edge out (the open side facing you), as this exposes the text block to dust and light.

Protection from Pests

Common Book Pests

Booklice (psocids) — tiny insects that feed on mold and sizing. They indicate high humidity.

Silverfish — nocturnal insects that feed on paper, adhesives, and sizing.

Bookworms — the larvae of various beetle species that bore through paper and bindings.

Rodents — mice and rats will nest in and eat paper, especially in attics, basements, and garages.

Prevention

• Maintain humidity below 60% (eliminates mold and deters insects)
• Keep storage areas clean and free of food
• Inspect incoming acquisitions for signs of active infestation
• Use integrated pest management (monitoring traps, environmental control) rather than chemical pesticides, which can damage books

Disaster Planning

Water

Water is the most immediate threat to books. Protect against:

• Plumbing failures — do not store books below water pipes; if unavoidable, cover shelves with plastic sheeting
• Flooding — store the most valuable books on upper shelves, not at floor level
• Roof leaks — inspect roofs regularly; place drip trays under known leak points

If books get wet:

1. Remove from water immediately
2. If frozen storage is available, freeze soaked books to prevent mold growth
3. Contact a professional conservator immediately
4. Do not attempt to dry wet books with heat (hairdryers, ovens) — this causes warping and cockling

Fire

• Install smoke detectors in and near storage areas
• Maintain fire extinguishers appropriate for paper fires (water-based, not dry chemical)
• Consider fire-resistant storage cabinets for the most valuable items
• Maintain adequate insurance

Proper storage is the simplest, most cost-effective form of preservation. The combination of stable temperature, controlled humidity, minimal light, and appropriate shelving will protect your books not just for your lifetime but for the lifetimes of future owners — an obligation that every serious collector accepts when they acquire a piece of our cultural heritage.