Grades 3–5 · History & Evidence
How could one handwritten line make a second copy?
Before office photocopiers became common, carbon paper could make a copy at the same time as an original letter. A thin coated sheet lay between the writing sheet and another sheet below. The coating faced the lower sheet.
In the diagramPressure makes a second markCoated transfer paper · layers pulled apart to showOriginalCarbon sheetCopy sheetPen pressesCoated side ↓The lower sheet receives dark coating.
As a pen pressed a line into the top sheet, that pressure passed through to the coating. Some dark material transferred onto the sheet underneath, following the pen’s path. The pen supplied ink to the original, while the carbon sheet supplied the material for the copy.
The arrangement mattered. Turning the coated face upward would mark the back of the original rather than the lower sheet. With no coating, pressure alone would not make the same dark copy. This was a physical transfer, not light passing through the paper.
Carbon copies preserved records without rewriting every word. They could also smudge or become faint as coating was used. Unlike a photocopier, this method did not simply copy any finished page: the marks needed pressure while the sheets were together.
About this explanation
Starting knowledge: Can follow a top, middle and bottom layer.
Sources
- Smithsonian Institution Archives — Preservation Photocopying: carbon-copy typescript
- National Museum of American History — Carbon paper, Crown Ribbon and Carbon Mfg. Co.