Why Do Old Calendars Start to Yellow Over Time?
What It Is
Older paper calendars often change from white to a yellow or tan color as they age, even when they have been kept indoors.
How It Works
Most paper is made from wood pulp, which contains a natural substance called lignin. Over time, lignin reacts with air and light.
This slow reaction changes the chemical structure of the paper, causing it to darken.
Why It Happens
- Lignin oxidation: Oxygen breaks down compounds in the paper.
- Light exposure: Sunlight and indoor lighting speed up color changes.
- Heat: Warm conditions accelerate aging reactions.
- Paper quality: Everyday paper yellows faster than archival paper.
Common Examples
- Old calendars turning yellow near the edges
- Paper pages becoming darker over time
- Stored calendars yellowing even without use
What to Know Next
Yellowing does not mean the calendar is dirty or damaged. It is a normal aging process for most paper products.
Simple Cautions
Paper stored in bright light or warm areas will usually yellow faster than paper kept in cooler, darker places.
Closing Summary
Old calendars turn yellow because chemicals in the paper react with light, air, and heat over time, slowly changing the paper’s color.
