---
title: "What is a Mirror made of?"
description: "A sheet of ordinary glass with a microscopically thin silver layer on the back, sealed under paint. Every component, the material it uses, and the constraint that ma"
url: https://atoneplace.net/made-of/mirror/
site: "At One Place"
---

# What is a Mirror made of?

**What is a Mirror made of?: A sheet of ordinary glass with a microscopically thin silver layer on the back, sealed under paint.**

Domestic mirrors are second-surface: light passes through the glass twice, so the front face of the glass produces a faint secondary reflection you can see by holding a pen against a mirror — the gap between the pen tip and its image is the glass thickness. Telescopes and precision optics cannot tolerate that, so they use front-surface mirrors, usually vacuum-deposited aluminium, which have to be handled with extreme care because there is no glass protecting the coating. Aluminium replaced silver for astronomy in the 1930s because it holds up better in air and reflects usefully into the ultraviolet, at the cost of a little visible reflectivity.

## Component by component

*Every material is a choice, and the third column is the constraint that drove it.*

| Part | Material | Why that material |
| --- | --- | --- |
| substrate | float glass, 3-6 mm | The glass is there for flatness and rigidity; the flatter it is, the less the reflection distorts. |
| reflective layer | silver, deposited chemically, well under a micrometre thick | Silver reflects over 95% across the visible spectrum, more than any other metal, but tarnishes instantly in air — hence the backing. |
| protective layers | a copper layer in older mirrors, or copper-free protective coats in modern ones | They stop oxygen and moisture reaching the silver from behind, which is what causes the black creeping edges of an old bathroom mirror. |
| backing paint | two coats of lead-free polymer paint | It seals the whole stack mechanically and chemically; scratching it is what kills a mirror. |
| optical mirrors | aluminium with a silicon dioxide overcoat, deposited on the front surface | A front-surface mirror avoids the faint double image that light reflecting off the glass front produces in an ordinary mirror. |

## Other building materials objects

- [Glass](https://atoneplace.net/made-of/glass/) — Sand melted with soda ash and limestone — three cheap minerals, floated flat on molten tin.
- [Concrete](https://atoneplace.net/made-of/concrete/) — Stone and sand glued by cement paste — and it hardens by a chemical reaction with water, not by drying.
- [MDF](https://atoneplace.net/made-of/mdf/) — Wood pulled apart into individual fibres, mixed with resin and wax, and pressed hot into a board.
- [Road asphalt](https://atoneplace.net/made-of/asphalt/) — About 95% crushed stone and sand, glued together by roughly 5% bitumen from the bottom of an oil refinery.
- [Brick](https://atoneplace.net/made-of/brick/) — Clay and shale moulded and fired until the particles partly fuse — a manufactured rock.
- [Plywood](https://atoneplace.net/made-of/plywood/) — Thin wood veneers glued in alternating grain directions — the cross-lamination is the entire idea.

## Common questions

### What is a Mirror made of?

A sheet of ordinary glass with a microscopically thin silver layer on the back, sealed under paint.

### What is the substrate of a Mirror made of?

Float glass, 3-6 mm. The glass is there for flatness and rigidity; the flatter it is, the less the reflection distorts.

### What is the reflective layer of a Mirror made of?

Silver, deposited chemically, well under a micrometre thick. Silver reflects over 95% across the visible spectrum, more than any other metal, but tarnishes instantly in air — hence the backing.

## Related pages

- [Glass](https://atoneplace.net/made-of/glass/)
- [Concrete](https://atoneplace.net/made-of/concrete/)
- [MDF](https://atoneplace.net/made-of/mdf/)
- [Road asphalt](https://atoneplace.net/made-of/asphalt/)
- [Brick](https://atoneplace.net/made-of/brick/)
- [Plywood](https://atoneplace.net/made-of/plywood/)
- [Pencil](https://atoneplace.net/made-of/pencil/)
- [Tennis ball](https://atoneplace.net/made-of/tennis-ball/)
- [Banknote](https://atoneplace.net/made-of/banknote/)
- [Golf ball](https://atoneplace.net/made-of/golf-ball/)
- [Paper](https://atoneplace.net/made-of/paper/)
- [Soccer ball](https://atoneplace.net/made-of/soccer-ball/)

## Sources

- Typical range compiled from manufacturer specifications — At One Place (/about/)