Hall–Héroult process and glasses: what they have in common

1. Step 1. Hall–Héroult process — uses — Carbon. The electrodes for smelting aluminium are carbon — they slowly burn away.
2. Step 2. Carbon — is material for — Photocopier. Toner is carbon black in resin.
3. Step 3. Photocopier — has part — Lens. Optics.
4. Step 4. Lens — is part of — Glasses. Lenses.

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