Covalent crystals are not necessarily opaque. Think of diamond, pure quartz crystals, pure aluminium oxide crystals these all are colorless and transparent.
Briefly, an LCD monitor uses thousands of tiny liquid crystals (the LC in LCD) as shutters that change from opaque to transparent depending on electricity applied to them. They let through white or colored light to form images, one tiny dot at a time. The dots are called pixels.
Thse crystals do not transmit light radiation.
crystals that ar opaque
Metallic crystals absorb light in the visible spectra, diamond crystal do not.
When light hits a transparent liquid crystal in a digital watch, it either passes through or gets reflected, depending on the electrical current applied to the crystal. Opaque liquid crystals block the light, preventing it from passing through. The manipulation of light by liquid crystals allows for the display of information in digital watches.
Ointments are a topical form that is often opaque in appearance. They have a thick and greasy consistency which can make them appear opaque when applied to the skin.
An opaque mixture of pigments dissolved in linseed oil and applied to a panel is called a stain. Stains come in a variety of colors and are used to help protect wood from rotting.
Wax can be either transparent or opaque, depending on its composition and how it is processed. Some waxes, such as paraffin wax, are transparent when melted but become opaque when solidified. Beeswax, on the other hand, is typically opaque.
Clouds are not opaque; they are actually translucent. This means that they allow some light to pass through but scatter and reflect most of it. Clouds appear white because sunlight is scattered by water droplets or ice crystals in the cloud.
Translucent since it is possible to monitor blood flow and pulse rate by placing a light source and photo detector either side of a finger. Opaque means totally barring the passage of light.
A coating of colored, opaque, or transparent material applied to ceramics before firing.