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Welcome to my kitchen. Today I’m going to attempt to make something 

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that is really vital for the Webb Telescope’s ability to see. 

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So, let’s give it a go! But first I have to make some distilled

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water.

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music

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music

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It’s a salt crystal! 

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Why Does

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Webb Use Salt Lenses?

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Who doesn’t love salt? It has a long and important

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history. Since it was once the only way to preserve food, 

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it also dictated trade routes. It was one of the most coveted and expensive minerals. 

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Today, we rely heavily on salt to keep

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our roads safe, and salty snacks at the best!

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Webb needs salt. 

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Not this tasty kind, but as a lens. 

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So there are different types of lenses. Mirrors are a reflective lens 

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that bend the light. And then there are transmissive lenses that allow light to pass

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through them. Here’s the kicker, visible light, it behaves

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differently than infrared light. 

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So glass absorbs infrared light. 

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But salt doesn’t. 

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The type of salt in here is sodium chloride, or NaCl. And even though

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it’s the most common type of salt on Earth, it is not the only kind. 

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Salts are more than something you sprinkle on your food. 

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A salt is a combination of two things. A positively charged element, 

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usually a metal from groups 1 or 2; and a negatively charged halide

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usually from groups 16 or 17. They get their charge 

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by either gaining or losing a negatively charged electron.

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Webb uses three kinds of salt lenses

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lithium fluoride, barium fluoride

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and zinc selenide. 

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Making these lenses happens to be pretty tricky. 

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I’ve been growing this one, now for about three weeks

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and it’s only this size, right here. 

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The lithium fluoride lenses that Webb uses

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have to be absolutely perfectly grown. 

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be optically useful, it needs to be completely clear

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unlike my homegrown crystal over here, and be molecularly 

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consistent. That means the structure of the molecules

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are absolutely the same everywhere. Then they have to be cut, and polished. 

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Considering what these lenses will do

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they are sure worth their weight in salt. 

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music