Solids:
* Wood: You can't see through a wooden table.
* Metal: A metal sheet blocks light from passing through it.
* Brick: A brick wall is opaque.
* Rock: Rocks are generally opaque, although some thin slices can be translucent.
* Paper: Most paper is opaque, though there are translucent varieties.
* Plastic: Many plastics are opaque, like a milk jug.
* Concrete: Concrete is a solid, opaque material.
Liquids:
* Milk: You can't see through a glass of milk.
* Paint: Paint is generally opaque, designed to cover surfaces.
* Coffee: A cup of coffee is opaque.
* Juice: Many juices, like orange juice, are opaque.
Gases:
* Smoke: Thick smoke is opaque.
* Fog: Fog is a dense cloud of water droplets in the air, making it opaque.
* Clouds: Clouds are opaque to sunlight, but translucent to moonlight.
Note: The level of opacity can vary depending on the thickness and composition of the material. For example, a thin sheet of metal might be translucent, while a thick piece of wood would be opaque.
